diff --git a/aclocal.m4 b/aclocal.m4
index 3105667e9da3..e365a9a22b9a 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -5,7 +5,6 @@ dnl
 
 builtin(include, build/autoconf/hooks.m4)dnl
 builtin(include, build/autoconf/config.status.m4)dnl
-builtin(include, build/autoconf/toolchain.m4)dnl
 builtin(include, build/autoconf/altoptions.m4)dnl
 
 # Read the user's .mozconfig script.  We can't do this in
diff --git a/build/autoconf/toolchain.m4 b/build/autoconf/toolchain.m4
deleted file mode 100644
index e0e856ad4c47..000000000000
--- a/build/autoconf/toolchain.m4
+++ /dev/null
@@ -1,58 +0,0 @@
-dnl This Source Code Form is subject to the terms of the Mozilla Public
-dnl License, v. 2.0. If a copy of the MPL was not distributed with this
-dnl file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-dnl Several autoconf functions AC_REQUIRE AC_PROG_CPP/AC_PROG_CXXCPP
-dnl or AC_HEADER_STDC, meaning they are called even when we don't call
-dnl them explicitly.
-dnl However, theses checks are not necessary and python configure sets
-dnl the corresponding variables already, so just skip those tests
-dnl entirely.
-define([AC_PROG_CPP],[])
-define([AC_PROG_CXXCPP],[])
-define([AC_HEADER_STDC], [])
-
-dnl AC_LANG_* set ac_link to the C/C++ compiler, which works fine with
-dnl gcc and clang, but not great with clang-cl, where the build system
-dnl currently expects to run the linker independently. So LDFLAGS are not
-dnl really adapted to be used with clang-cl, which then proceeds to
-dnl execute link.exe rather than lld-link.exe.
-dnl So when the compiler is clang-cl, we modify ac_link to use a separate
-dnl linker call.
-define([_MOZ_AC_LANG_C], defn([AC_LANG_C]))
-define([AC_LANG_C],
-[_MOZ_AC_LANG_C
-if test "$CC_TYPE" = "clang-cl"; then
-  ac_link="$ac_compile"' && ${LINKER} -OUT:conftest${ac_exeext} $LDFLAGS conftest.obj $LIBS 1>&AC_FD_CC'
-fi
-])
-
-define([_MOZ_AC_LANG_CPLUSPLUS], defn([AC_LANG_CPLUSPLUS]))
-define([AC_LANG_CPLUSPLUS],
-[_MOZ_AC_LANG_CPLUSPLUS
-if test "$CC_TYPE" = "clang-cl"; then
-  ac_link="$ac_compile"' && ${LINKER} -OUT:conftest${ac_exeext} $LDFLAGS conftest.obj $LIBS 1>&AC_FD_CC'
-fi
-])
-
-
-AC_DEFUN([MOZ_CROSS_COMPILER],
-[
-echo "cross compiling from $host to $target"
-
-dnl AC_CHECK_PROGS manually goes through $PATH, and as such fails to handle
-dnl absolute or relative paths. Relative paths wouldn't work anyways, but
-dnl absolute paths would. Trick AC_CHECK_PROGS into working in that case by
-dnl adding / to PATH. This is temporary until this moves to moz.configure
-dnl (soon).
-_SAVE_PATH=$PATH
-case "${TOOLCHAIN_PREFIX}" in
-/*)
-    PATH="/:$PATH"
-    ;;
-esac
-AC_PROG_CC
-AC_PROG_CXX
-
-PATH=$_SAVE_PATH
-])
diff --git a/build/moz.configure/toolchain.configure b/build/moz.configure/toolchain.configure
index 0ea9135dba46..e97978147cdd 100644
--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -1713,12 +1713,21 @@ def compiler(
     # Set CC/CXX/HOST_CC/HOST_CXX for old-configure, which needs the wrapper
     # and the flags that were part of the user input for those variables to
     # be provided.
-    add_old_configure_assignment(
-        var,
-        depends_if(valid_compiler)(
-            lambda x: list(x.wrapper) + [x.compiler] + list(x.flags)
-        ),
-    )
+    if var in ("CC", "CXX"):
+        # FIXME: we should return a plain list here.
+        @depends_if(valid_compiler)
+        @imports(_from="mozbuild.shellutil", _import="quote")
+        def value(x):
+            return quote(*x.wrapper, x.compiler, *x.flags)
+
+        set_config(var, value)
+    else:
+        add_old_configure_assignment(
+            var,
+            depends_if(valid_compiler)(
+                lambda x: list(x.wrapper) + [x.compiler] + list(x.flags)
+            ),
+        )
 
     if host_or_target is target:
         add_old_configure_assignment(
diff --git a/js/src/aclocal.m4 b/js/src/aclocal.m4
index 37bfafda550e..4151cbd8878b 100644
--- a/js/src/aclocal.m4
+++ b/js/src/aclocal.m4
@@ -5,7 +5,6 @@ dnl
 
 builtin(include, ../../build/autoconf/hooks.m4)dnl
 builtin(include, ../../build/autoconf/config.status.m4)dnl
-builtin(include, ../../build/autoconf/toolchain.m4)dnl
 builtin(include, ../../build/autoconf/altoptions.m4)dnl
 
 define([__MOZ_AC_INIT_PREPARE], defn([AC_INIT_PREPARE]))
diff --git a/js/src/old-configure.in b/js/src/old-configure.in
index 9ea8d8652abf..f388d4c4058c 100644
--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -16,35 +16,6 @@ if test -z "$JS_STANDALONE"; then
 fi
 AC_SUBST(autoconfmk)
 
-dnl ========================================================
-dnl Checks for compilers.
-dnl ========================================================
-
-if test "$COMPILE_ENVIRONMENT"; then
-
-# This prevents mingw from adding .exe when generating executable. Internal use
-# only.
-ac_exeext=.out
-
-# Note:
-#   In Mozilla, we use the names $target, $host and $build incorrectly, but are
-#   too far gone to back out now. See Bug 475488:
-#     - When we say $target, we mean $host, that is, the system on which
-#       Mozilla will be run.
-#     - When we say $host, we mean $build, that is, the system on which Mozilla
-#       is built.
-#     - $target (in its correct usage) is for compilers who generate code for a
-#       different platform than $host, so it would not be used by Mozilla.
-if test "$target" != "$host"; then
-    MOZ_CROSS_COMPILER
-else
-    AC_PROG_CC
-    AC_PROG_CXX
-fi
-
-fi # COMPILE_ENVIRONMENT
-
-
 dnl ========================================================
 dnl =
 dnl = Maintainer debug option (no --enable equivalent)
diff --git a/old-configure.in b/old-configure.in
index 34fff2d451e3..3e43cf6a10d9 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -11,30 +11,6 @@ AC_INIT(config/config.mk)
 AC_CONFIG_AUX_DIR(${srcdir}/build/autoconf)
 AC_CANONICAL_SYSTEM
 
-dnl ========================================================
-dnl Checks for compilers.
-dnl ========================================================
-
-if test "$COMPILE_ENVIRONMENT"; then
-
-# This prevents mingw from adding .exe when generating executable. Internal use
-# only.
-ac_exeext=.out
-
-if test "$target" != "$host"; then
-    MOZ_CROSS_COMPILER
-else
-    AC_PROG_CC
-    case "$target" in
-    *-mingw*)
-      # Work around the conftest.exe access problem on Windows
-      sleep 2
-    esac
-    AC_PROG_CXX
-fi
-
-fi # COMPILE_ENVIRONMENT
-
 dnl ========================================================
 dnl =
 dnl = Application