Use MSVC compiler flags only with MSVC

Author: mimi89999

CMakeLists.txt

@@ -13,8 +13,18 @@ set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
 
-# TODO: re-enable /GL and /LTCG when we get a bigger build machine
-add_compile_options(/bigobj /GR- /permissive-)
+if (MSVC)
+    # TODO: re-enable /GL and /LTCG when we get a bigger build machine
+    add_compile_options(/bigobj /GR- /permissive-)
+
+    string(REGEX REPLACE "/GR" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+    # TODO: re-enable /GL and /LTCG when we get a bigger build machine
+    # string(APPEND CMAKE_MODULE_LINKER_FLAGS " /LTCG:STATUS")
+
+    if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "19.20.27404.0")
+        string(APPEND CMAKE_CXX_FLAGS " /d2FH4")
+    endif()
+endif()
 
 # strip suffix to allow support for prerelease version
 string(REGEX MATCH "^[0-9]\\.[0-9]+(\\.[0-9]+)?" PYTHON_BASE_VERSION ${PYTHON_VERSION_STRING})
@@ -34,12 +44,4 @@ if($ENV{CI})
     set_property(TARGET _winrt PROPERTY JOB_POOL_COMPILE compile_job)
 endif()
 
-string(REGEX REPLACE "/GR" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
-# TODO: re-enable /GL and /LTCG when we get a bigger build machine
-# string(APPEND CMAKE_MODULE_LINKER_FLAGS " /LTCG:STATUS")
-
-if (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "19.20.27404.0")
-    string(APPEND CMAKE_CXX_FLAGS " /d2FH4")
-endif()
-
 install(TARGETS _winrt DESTINATION "pywinrt/${CMAKE_PROJECT_NAME}")