clang: Work around toolchain file use of internal CMake variables
Since commit d44c0db0b2 (clang: setup correct configuration in gnu mode,
2019-02-20, v3.15.0-rc1~41^2~5) our Clang compiler information modules
need the `CMAKE_<LANG>_COMPILER_FRONTEND_VARIANT` variable that we
compute during compiler detection. However, some existing toolchain
files set our internal `CMAKE_<LANG>_COMPILER_ID_RUN` variables and
block that detection, but do not set the new frontend variant variable.
Help them out by setting `CMAKE_<LANG>_COMPILER_FRONTEND_VARIANT` anyway.
Fixes: #19515, #19539
diff --git a/Modules/CMakeDetermineCCompiler.cmake b/Modules/CMakeDetermineCCompiler.cmake
index 8be781a..037c33b 100644
--- a/Modules/CMakeDetermineCCompiler.cmake
+++ b/Modules/CMakeDetermineCCompiler.cmake
@@ -124,6 +124,22 @@
elseif(CMAKE_C_PLATFORM_ID MATCHES "Cygwin")
set(CMAKE_COMPILER_IS_CYGWIN 1)
endif()
+else()
+ if(NOT DEFINED CMAKE_C_COMPILER_FRONTEND_VARIANT)
+ # Some toolchain files set our internal CMAKE_C_COMPILER_ID_RUN
+ # variable but are not aware of CMAKE_C_COMPILER_FRONTEND_VARIANT.
+ # They pre-date our support for the GNU-like variant targeting the
+ # MSVC ABI so we do not consider that here.
+ if(CMAKE_C_COMPILER_ID STREQUAL "Clang")
+ if("x${CMAKE_C_SIMULATE_ID}" STREQUAL "xMSVC")
+ set(CMAKE_C_COMPILER_FRONTEND_VARIANT "MSVC")
+ else()
+ set(CMAKE_C_COMPILER_FRONTEND_VARIANT "GNU")
+ endif()
+ else()
+ set(CMAKE_C_COMPILER_FRONTEND_VARIANT "")
+ endif()
+ endif()
endif()
if (NOT _CMAKE_TOOLCHAIN_LOCATION)
diff --git a/Modules/CMakeDetermineCXXCompiler.cmake b/Modules/CMakeDetermineCXXCompiler.cmake
index 00ef5b9..7274eec 100644
--- a/Modules/CMakeDetermineCXXCompiler.cmake
+++ b/Modules/CMakeDetermineCXXCompiler.cmake
@@ -119,6 +119,22 @@
elseif(CMAKE_CXX_PLATFORM_ID MATCHES "Cygwin")
set(CMAKE_COMPILER_IS_CYGWIN 1)
endif()
+else()
+ if(NOT DEFINED CMAKE_CXX_COMPILER_FRONTEND_VARIANT)
+ # Some toolchain files set our internal CMAKE_CXX_COMPILER_ID_RUN
+ # variable but are not aware of CMAKE_CXX_COMPILER_FRONTEND_VARIANT.
+ # They pre-date our support for the GNU-like variant targeting the
+ # MSVC ABI so we do not consider that here.
+ if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+ if("x${CMAKE_CXX_SIMULATE_ID}" STREQUAL "xMSVC")
+ set(CMAKE_CXX_COMPILER_FRONTEND_VARIANT "MSVC")
+ else()
+ set(CMAKE_CXX_COMPILER_FRONTEND_VARIANT "GNU")
+ endif()
+ else()
+ set(CMAKE_CXX_COMPILER_FRONTEND_VARIANT "")
+ endif()
+ endif()
endif()
if (NOT _CMAKE_TOOLCHAIN_LOCATION)
