CheckLanguage: Fix forwarding of CMAKE_CUDA_HOST_COMPILER

Fix the condition added by commit 58278a1ecd (CheckLanguage: Report
CMAKE_CUDA_HOST_COMPILER if needed for compilation, 2019-05-31,
v3.15.0-rc1~12^2) to activate CUDA-specific logic.  The old condition
had worked in our test suite only by accident because the loop variable
used in the test happened to be the name and value that the old
condition used!  Update the test to use a different name.

Fixes: #19013

Modules/CheckLanguage.cmake

@@ -43,7 +43,7 @@ macro(check_language lang)
     file(REMOVE_RECURSE ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/Check${lang})
 
     set(extra_compiler_variables)
-    if(lang STREQUAL CUDA)
+    if(${lang} STREQUAL CUDA)
       set(extra_compiler_variables "set(CMAKE_CUDA_HOST_COMPILER \\\"\${CMAKE_CUDA_HOST_COMPILER}\\\")")
     endif()
 

Tests/CMakeOnly/CheckLanguage/CMakeLists.txt

@@ -18,16 +18,16 @@ if(APPLE)
   list(APPEND LANGUAGES OBJC OBJCXX)
 endif()
 
-foreach(lang ${LANGUAGES})
-  check_language(${lang})
-  if(NOT DEFINED CMAKE_${lang}_COMPILER)
-    message(FATAL_ERROR "check_language(${lang}) did not set result")
+foreach(test_lang ${LANGUAGES})
+  check_language(${test_lang})
+  if(NOT DEFINED CMAKE_${test_lang}_COMPILER)
+    message(FATAL_ERROR "check_language(${test_lang}) did not set result")
   endif()
-  if(DEFINED expect_${lang})
-    if(expect_${lang} AND NOT CMAKE_${lang}_COMPILER)
-      message(FATAL_ERROR "check_language(${lang}) should not fail!")
-    elseif(NOT expect_${lang} AND CMAKE_${lang}_COMPILER)
-      message(FATAL_ERROR "check_language(${lang}) should not succeed!")
+  if(DEFINED expect_${test_lang})
+    if(expect_${test_lang} AND NOT CMAKE_${test_lang}_COMPILER)
+      message(FATAL_ERROR "check_language(${test_lang}) should not fail!")
+    elseif(NOT expect_${test_lang} AND CMAKE_${test_lang}_COMPILER)
+      message(FATAL_ERROR "check_language(${test_lang}) should not succeed!")
     endif()
   endif()
 endforeach()