diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index eb19646646f0..015a359bfb48 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -397,11 +397,9 @@ endif ()
 # Configure System
 #===============================================================================
 
-# TODO: Other projects rely on the location where we generate the libc++ headers
-#       internally. We should get rid of these dependencies.
 if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
   set(LIBCXX_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR}/${LLVM_DEFAULT_TARGET_TRIPLE}/c++)
-  set(LIBCXX_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
+  set(LIBCXX_HEADER_DIR ${LLVM_BINARY_DIR})
   set(LIBCXX_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE}/c++)
   if(LIBCXX_LIBDIR_SUBDIR)
     string(APPEND LIBCXX_LIBRARY_DIR /${LIBCXX_LIBDIR_SUBDIR})
@@ -409,11 +407,11 @@ if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
   endif()
 elseif(LLVM_LIBRARY_OUTPUT_INTDIR)
   set(LIBCXX_LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
-  set(LIBCXX_GENERATED_INCLUDE_DIR  "${LLVM_BINARY_DIR}/include/c++/v1")
+  set(LIBCXX_HEADER_DIR  ${LLVM_BINARY_DIR})
   set(LIBCXX_INSTALL_LIBRARY_DIR lib${LIBCXX_LIBDIR_SUFFIX})
 else()
   set(LIBCXX_LIBRARY_DIR ${CMAKE_BINARY_DIR}/lib${LIBCXX_LIBDIR_SUFFIX})
-  set(LIBCXX_GENERATED_INCLUDE_DIR  "${CMAKE_BINARY_DIR}/include/c++/v1")
+  set(LIBCXX_HEADER_DIR  ${CMAKE_BINARY_DIR})
   set(LIBCXX_INSTALL_LIBRARY_DIR lib${LIBCXX_LIBDIR_SUFFIX})
 endif()
 
diff --git a/libcxx/benchmarks/CMakeLists.txt b/libcxx/benchmarks/CMakeLists.txt
index 12acffcbc98b..42d25c20c811 100644
--- a/libcxx/benchmarks/CMakeLists.txt
+++ b/libcxx/benchmarks/CMakeLists.txt
@@ -8,7 +8,7 @@ include(CheckCXXCompilerFlag)
 set(BENCHMARK_LIBCXX_COMPILE_FLAGS
     -Wno-unused-command-line-argument
     -nostdinc++
-    -isystem "${LIBCXX_GENERATED_INCLUDE_DIR}"
+    -isystem ${LIBCXX_SOURCE_DIR}/include
     -L${LIBCXX_LIBRARY_DIR}
     -Wl,-rpath,${LIBCXX_LIBRARY_DIR}
     ${SANITIZER_FLAGS}
@@ -18,6 +18,7 @@ if (DEFINED LIBCXX_CXX_ABI_LIBRARY_PATH)
           -L${LIBCXX_CXX_ABI_LIBRARY_PATH}
           -Wl,-rpath,${LIBCXX_CXX_ABI_LIBRARY_PATH})
 endif()
+list(APPEND BENCHMARK_LIBCXX_COMPILE_FLAGS -include "${LIBCXX_BINARY_DIR}/__config_site")
 split_list(BENCHMARK_LIBCXX_COMPILE_FLAGS)
 
 ExternalProject_Add(google-benchmark-libcxx
diff --git a/libcxx/cmake/Modules/HandleLibCXXABI.cmake b/libcxx/cmake/Modules/HandleLibCXXABI.cmake
index 6f50853189a2..c5aa26739e36 100644
--- a/libcxx/cmake/Modules/HandleLibCXXABI.cmake
+++ b/libcxx/cmake/Modules/HandleLibCXXABI.cmake
@@ -52,10 +52,8 @@ macro(setup_abi_lib abidefines abishared abistatic abifiles abidirs)
             COMMENT "Copying C++ ABI header ${fpath}...")
         list(APPEND abilib_headers "${dst}")
 
-        if (LIBCXX_GENERATED_INCLUDE_DIR) # always true
-          # TODO: libc++ shouldn't be responsible for copying the libc++abi
-          #       headers into the right location.
-          set(dst "${LIBCXX_GENERATED_INCLUDE_DIR}/include/c++/v1/${dstdir}/${fpath}")
+        if (LIBCXX_HEADER_DIR)
+          set(dst "${LIBCXX_HEADER_DIR}/include/c++/v1/${dstdir}/${fpath}")
           add_custom_command(OUTPUT ${dst}
               DEPENDS ${src}
               COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
diff --git a/libcxx/docs/TestingLibcxx.rst b/libcxx/docs/TestingLibcxx.rst
index ec017e23b147..d42becfd5c3d 100644
--- a/libcxx/docs/TestingLibcxx.rst
+++ b/libcxx/docs/TestingLibcxx.rst
@@ -26,8 +26,8 @@ Usage
 
 After building libc++, you can run parts of the libc++ test suite by simply
 running ``llvm-lit`` on a specified test or directory. If you're unsure
-whether the required targets have been built, you can use the `check-cxx-deps`
-target to build them. For example:
+whether the required libraries have been built, you can use the
+`check-cxx-deps` target. For example:
 
 .. code-block:: bash
 
@@ -37,12 +37,6 @@ target to build them. For example:
   $ <build>/bin/llvm-lit -sv libcxx/test/std/depr/depr.c.headers/stdlib_h.pass.cpp # Run a single test
   $ <build>/bin/llvm-lit -sv libcxx/test/std/atomics libcxx/test/std/threads # Test std::thread and std::atomic
 
-In the default configuration, the tests are built against headers that form a
-fake installation root of libc++. This installation root has to be updated when
-changes are made to the headers, so you should re-run the `check-cxx-deps` target
-before running the tests manually with `lit` when you make any sort of change,
-including to the headers.
-
 Sometimes you'll want to change the way LIT is running the tests. Custom options
 can be specified using the `--param=<name>=<val>` flag. The most common option
 you'll want to change is the standard dialect (ie -std=c++XX). By default the
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index a63b565e4400..7c97db41bb73 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -2,7 +2,6 @@ set(files
   __bit_reference
   __bsd_locale_defaults.h
   __bsd_locale_fallbacks.h
-  __config
   __errc
   __debug
   __functional_03
@@ -185,28 +184,62 @@ if(LIBCXX_INSTALL_SUPPORT_HEADERS)
     )
 endif()
 
-if (LIBCXX_GENERATED_INCLUDE_DIR) # Always true
-  configure_file("__config_site.in" "${LIBCXX_GENERATED_INCLUDE_DIR}/__config_site" @ONLY)
+configure_file("__config_site.in"
+               "${LIBCXX_BINARY_DIR}/__config_site"
+               @ONLY)
 
-  set(_all_includes "${LIBCXX_GENERATED_INCLUDE_DIR}/__config_site")
+# Generate a custom __config header. The new header is created
+# by prepending __config_site to the current __config header.
+add_custom_command(OUTPUT ${LIBCXX_BINARY_DIR}/__generated_config
+  COMMAND ${Python3_EXECUTABLE} ${LIBCXX_SOURCE_DIR}/utils/cat_files.py
+    ${LIBCXX_BINARY_DIR}/__config_site
+    ${LIBCXX_SOURCE_DIR}/include/__config
+    -o ${LIBCXX_BINARY_DIR}/__generated_config
+  DEPENDS ${LIBCXX_SOURCE_DIR}/include/__config
+          ${LIBCXX_BINARY_DIR}/__config_site
+)
+# Add a target that executes the generation commands.
+add_custom_target(cxx-generated-config ALL
+  DEPENDS ${LIBCXX_BINARY_DIR}/__generated_config)
+
+if(LIBCXX_HEADER_DIR)
+  set(output_dir ${LIBCXX_HEADER_DIR}/include/c++/v1)
+
+  set(out_files)
   foreach(f ${files})
-    set(src "${CMAKE_CURRENT_SOURCE_DIR}/${f}")
-    set(dst "${LIBCXX_GENERATED_INCLUDE_DIR}/${f}")
+    set(src ${CMAKE_CURRENT_SOURCE_DIR}/${f})
+    set(dst ${output_dir}/${f})
     add_custom_command(OUTPUT ${dst}
       DEPENDS ${src}
       COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
       COMMENT "Copying CXX header ${f}")
-    list(APPEND _all_includes "${dst}")
+    list(APPEND out_files ${dst})
   endforeach()
-  add_custom_target(generate-cxx-headers DEPENDS ${_all_includes})
+
+  # Copy the generated header as __config into build directory.
+  set(src ${LIBCXX_BINARY_DIR}/__generated_config)
+  set(dst ${output_dir}/__config)
+  add_custom_command(OUTPUT ${dst}
+      DEPENDS ${src} cxx-generated-config
+      COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
+      COMMENT "Copying CXX __config")
+  list(APPEND out_files ${dst})
+  add_custom_target(generate-cxx-headers DEPENDS ${out_files})
 
   add_library(cxx-headers INTERFACE)
   add_dependencies(cxx-headers generate-cxx-headers ${LIBCXX_CXX_ABI_HEADER_TARGET})
   # TODO: Use target_include_directories once we figure out why that breaks the runtimes build
   if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
-    target_compile_options(cxx-headers INTERFACE /I "${LIBCXX_GENERATED_INCLUDE_DIR}")
+    target_compile_options(cxx-headers INTERFACE /I "${output_dir}")
   else()
-    target_compile_options(cxx-headers INTERFACE -I "${LIBCXX_GENERATED_INCLUDE_DIR}")
+    target_compile_options(cxx-headers INTERFACE -I "${output_dir}")
+  endif()
+
+  # Make sure the generated __config_site header is included when we build the library.
+  if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
+    target_compile_options(cxx-headers INTERFACE /FI "${LIBCXX_BINARY_DIR}/__config_site")
+  else()
+    target_compile_options(cxx-headers INTERFACE -include "${LIBCXX_BINARY_DIR}/__config_site")
   endif()
 else()
   add_library(cxx-headers INTERFACE)
@@ -222,15 +255,16 @@ if (LIBCXX_INSTALL_HEADERS)
     )
   endforeach()
 
-  # Install the generated __config_site.
-  install(FILES ${LIBCXX_GENERATED_INCLUDE_DIR}/__config_site
+  # Install the generated header as __config.
+  install(FILES ${LIBCXX_BINARY_DIR}/__generated_config
     DESTINATION ${LIBCXX_INSTALL_HEADER_PREFIX}include/c++/v1
     PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
+    RENAME __config
     COMPONENT cxx-headers)
 
   if (NOT CMAKE_CONFIGURATION_TYPES)
     add_custom_target(install-cxx-headers
-                      DEPENDS cxx-headers
+                      DEPENDS cxx-headers cxx-generated-config
                       COMMAND "${CMAKE_COMMAND}"
                               -DCMAKE_INSTALL_COMPONENT=cxx-headers
                               -P "${CMAKE_BINARY_DIR}/cmake_install.cmake")
diff --git a/libcxx/include/__config b/libcxx/include/__config
index f2ebd4d167d9..7cdcd9a7275e 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -10,8 +10,6 @@
 #ifndef _LIBCPP_CONFIG
 #define _LIBCPP_CONFIG
 
-#include <__config_site>
-
 #if defined(_MSC_VER) && !defined(__clang__)
 #  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #    define _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
diff --git a/libcxx/test/configs/legacy.cfg.in b/libcxx/test/configs/legacy.cfg.in
index 148ac3fc5a89..f0a4e8a73e09 100644
--- a/libcxx/test/configs/legacy.cfg.in
+++ b/libcxx/test/configs/legacy.cfg.in
@@ -3,7 +3,6 @@
 import os
 import site
 
-config.cxx_headers              = "@LIBCXX_GENERATED_INCLUDE_DIR@"
 config.cxx_under_test           = "@CMAKE_CXX_COMPILER@"
 config.project_obj_root         = "@CMAKE_BINARY_DIR@"
 config.libcxx_src_root          = "@LIBCXX_SOURCE_DIR@"
diff --git a/libcxx/utils/libcxx/test/config.py b/libcxx/utils/libcxx/test/config.py
index c5050d1b6b9a..0d21aa17afd2 100644
--- a/libcxx/utils/libcxx/test/config.py
+++ b/libcxx/utils/libcxx/test/config.py
@@ -331,6 +331,7 @@ class Configuration(object):
 
     def configure_compile_flags_header_includes(self):
         support_path = os.path.join(self.libcxx_src_root, 'test', 'support')
+        self.configure_config_site_header()
         if self.cxx_stdlib_under_test != 'libstdc++' and \
            not self.target_info.is_windows():
             self.cxx.compile_flags += [
@@ -347,12 +348,16 @@ class Configuration(object):
                                          'set_windows_crt_report_mode.h')
             ]
         cxx_headers = self.get_lit_conf('cxx_headers')
-        if cxx_headers is None and self.cxx_stdlib_under_test != 'libc++':
+        if cxx_headers == '' or (cxx_headers is None
+                                 and self.cxx_stdlib_under_test != 'libc++'):
             self.lit_config.note('using the system cxx headers')
             return
         self.cxx.compile_flags += ['-nostdinc++']
+        if cxx_headers is None:
+            cxx_headers = os.path.join(self.libcxx_src_root, 'include')
         if not os.path.isdir(cxx_headers):
-            self.lit_config.fatal("cxx_headers='{}' is not a directory.".format(cxx_headers))
+            self.lit_config.fatal("cxx_headers='%s' is not a directory."
+                                  % cxx_headers)
         self.cxx.compile_flags += ['-I' + cxx_headers]
         if self.libcxx_obj_root is not None:
             cxxabi_headers = os.path.join(self.libcxx_obj_root, 'include',
@@ -360,6 +365,16 @@ class Configuration(object):
             if os.path.isdir(cxxabi_headers):
                 self.cxx.compile_flags += ['-I' + cxxabi_headers]
 
+    def configure_config_site_header(self):
+        # Check for a possible __config_site in the build directory. We
+        # use this if it exists.
+        if self.libcxx_obj_root is None:
+            return
+        config_site_header = os.path.join(self.libcxx_obj_root, '__config_site')
+        if not os.path.isfile(config_site_header):
+            return
+        self.cxx.compile_flags += ['-include', config_site_header]
+
     def configure_link_flags(self):
         # Configure library path
         self.configure_link_flags_cxx_library_path()
diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
index a5d3a06a20a6..3f37dbf4cd36 100644
--- a/libcxxabi/CMakeLists.txt
+++ b/libcxxabi/CMakeLists.txt
@@ -138,23 +138,9 @@ if (NOT LIBCXXABI_ENABLE_SHARED AND NOT LIBCXXABI_ENABLE_STATIC)
   message(FATAL_ERROR "libc++abi must be built as either a shared or static library.")
 endif()
 
-# TODO: This is a hack for the fact that Standalone builds can't use targets
-#       from the other runtimes (so the cxx-headers target doesn't exist).
-set(LIBCXXABI_LIBCXX_INCLUDES "" CACHE PATH
-    "Specify path to the installed libc++ includes. This is only relevant for Standalone builds, where the location of the headers can't be determined automatically.")
-if (LIBCXXABI_STANDALONE_BUILD)
-  if (NOT IS_DIRECTORY ${LIBCXXABI_LIBCXX_INCLUDES})
-    message(FATAL_ERROR
-      "LIBCXXABI_LIBCXX_INCLUDES=${LIBCXXABI_LIBCXX_INCLUDES} is not a valid directory. "
-      "Please provide the path to where the libc++ headers have been installed.")
-  endif()
-  add_library(cxx-headers INTERFACE)
-  if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC" OR "${CMAKE_CXX_SIMULATE_ID}" STREQUAL "MSVC")
-    target_compile_options(cxx-headers INTERFACE /I "${LIBCXXABI_LIBCXX_INCLUDES}")
-  else()
-    target_compile_options(cxx-headers INTERFACE -I "${LIBCXXABI_LIBCXX_INCLUDES}")
-  endif()
-endif()
+set(LIBCXXABI_LIBCXX_INCLUDES "${LIBCXXABI_LIBCXX_PATH}/include" CACHE PATH
+    "Specify path to libc++ includes.")
+message(STATUS "Libc++abi will be using libc++ includes from ${LIBCXXABI_LIBCXX_INCLUDES}")
 
 option(LIBCXXABI_HERMETIC_STATIC_LIBRARY
   "Do not export any symbols from the static library." OFF)
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
index 8d4d84c225e2..e9e454082a05 100644
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -55,6 +55,8 @@ if (MSVC_IDE OR XCODE)
   endif()
 endif()
 
+include_directories("${LIBCXXABI_LIBCXX_INCLUDES}")
+
 if (LIBCXXABI_HAS_CXA_THREAD_ATEXIT_IMPL)
   add_definitions(-DHAVE___CXA_THREAD_ATEXIT_IMPL)
 endif()
@@ -166,7 +168,7 @@ if (LIBCXXABI_ENABLE_SHARED)
   if(COMMAND llvm_setup_rpath)
     llvm_setup_rpath(cxxabi_shared)
   endif()
-  target_link_libraries(cxxabi_shared PRIVATE cxx-headers ${LIBCXXABI_SHARED_LIBRARIES} ${LIBCXXABI_LIBRARIES})
+  target_link_libraries(cxxabi_shared PRIVATE ${LIBCXXABI_SHARED_LIBRARIES} ${LIBCXXABI_LIBRARIES})
   if (TARGET pstl::ParallelSTL)
     target_link_libraries(cxxabi_shared PUBLIC pstl::ParallelSTL)
   endif()
@@ -231,7 +233,7 @@ endif()
 # Build the static library.
 if (LIBCXXABI_ENABLE_STATIC)
   add_library(cxxabi_static STATIC ${LIBCXXABI_SOURCES} ${LIBCXXABI_HEADERS})
-  target_link_libraries(cxxabi_static PRIVATE cxx-headers ${LIBCXXABI_STATIC_LIBRARIES} ${LIBCXXABI_LIBRARIES})
+  target_link_libraries(cxxabi_static PRIVATE ${LIBCXXABI_STATIC_LIBRARIES} ${LIBCXXABI_LIBRARIES})
   if (TARGET pstl::ParallelSTL)
     target_link_libraries(cxxabi_static PUBLIC pstl::ParallelSTL)
   endif()
diff --git a/libcxxabi/test/libcxxabi/test/config.py b/libcxxabi/test/libcxxabi/test/config.py
index f9e17e9f97da..45fb0f5d7afc 100644
--- a/libcxxabi/test/libcxxabi/test/config.py
+++ b/libcxxabi/test/libcxxabi/test/config.py
@@ -56,8 +56,10 @@ class Configuration(LibcxxConfiguration):
         super(Configuration, self).configure_compile_flags()
 
     def configure_compile_flags_header_includes(self):
-        cxx_headers = self.get_lit_conf('cxx_headers', None) or \
-                    os.path.join(self.project_obj_root, 'include', 'c++', 'v1')
+        self.configure_config_site_header()
+        cxx_headers = self.get_lit_conf(
+            'cxx_headers',
+            os.path.join(self.libcxx_src_root, '/include'))
         if cxx_headers == '':
             self.lit_config.note('using the systems c++ headers')
         else:
diff --git a/libunwind/test/libunwind/test/config.py b/libunwind/test/libunwind/test/config.py
index 183c48f6a801..977f9a0fb3f9 100644
--- a/libunwind/test/libunwind/test/config.py
+++ b/libunwind/test/libunwind/test/config.py
@@ -49,6 +49,8 @@ class Configuration(LibcxxConfiguration):
         super(Configuration, self).configure_compile_flags()
 
     def configure_compile_flags_header_includes(self):
+        self.configure_config_site_header()
+
         libunwind_headers = self.get_lit_conf(
             'libunwind_headers',
             os.path.join(self.libunwind_src_root, 'include'))
diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
index 9d8222b14991..598daa4502e1 100644
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -133,13 +133,11 @@ if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
     string(REPLACE "-" "_" canon_name ${projName})
     string(TOUPPER ${canon_name} canon_name)
 
-    # compiler-rt needs to treat this as standalone builds. D57992 tried
-    # to get rid of it for compiler-rt, but it treats *_STANDALONE_BUILD=OFF
-    # as if llvm & clang are configured in the same CMake, and setup dependencies
+    # The subdirectories need to treat this as standalone builds. D57992 tried
+    # to get rid of this, but the runtimes treat *_STANDALONE_BUILD=OFF as if
+    # llvm & clang are configured in the same CMake, and setup dependencies
     # against their targets.
-    if ("${canon_name}" STREQUAL "COMPILER_RT")
-      set(${canon_name}_STANDALONE_BUILD ON)
-    endif()
+    set(${canon_name}_STANDALONE_BUILD ON)
 
     if(LLVM_RUNTIMES_LIBDIR_SUBDIR)
       set(${canon_name}_LIBDIR_SUBDIR "${LLVM_RUNTIMES_LIBDIR_SUBDIR}" CACHE STRING "" FORCE)