Use Modern CMake features instead of CMAKE_CXX_FLAGS (#24861)

* Convert C++ standard settings and warning options from CMAKE_<LANG>_FLAGS to Modern CMake isms.

* More $<COMPILE_LANGUAGE> generator expressions instead of CMAKE_CXX_FLAGS.

* Use $<COMPILE_LANGUAGE:CXX> for all -fpermissive usage

* Fix generator expression that generates multiple flags

* Fix invalid use of CMAKE_CXX_FLAGS instead of CMAKE_C_FLAGS.

* Treat AppleClang as though it is Clang (match pre-3.0 behavior).

* Update our build system to understand that AppleClang is distinct from Clang and remove CMP0025 policy setting.

* PR Feedback.

3 files changed, 6 insertions, 6 deletions

diff --git a/src/pal/src/libunwind/src/CMakeLists.txt b/src/pal/src/libunwind/src/CMakeLists.txt
index b29e7ee9a2..93b4daf3a6 100644
--- a/src/pal/src/libunwind/src/CMakeLists.txt
+++ b/src/pal/src/libunwind/src/CMakeLists.txt
@@ -22,7 +22,7 @@ add_definitions("-Ddwarf_search_unwind_table_int=UNW_OBJ(dwarf_search_unwind_tab
 # Disable warning due to incorrect format specifier in debugging printf via the Debug macro
 add_compile_options(-Wno-format)
 
-if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   add_compile_options(-Wno-header-guard)
 elseif()
   add_compile_options(-Wno-unused-value)
@@ -33,7 +33,7 @@ if(CLR_CMAKE_PLATFORM_ARCH_ARM)
     add_definitions("-Darm_search_unwind_table=UNW_OBJ(arm_search_unwind_table)")
     # Disable warning in asm: use of SP or PC in the list is deprecated
     add_compile_options(-Wno-inline-asm)
-    if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
         # Disable warning due to labs function called on unsigned argument
         add_compile_options(-Wno-absolute-value)
     endif()
@@ -48,7 +48,7 @@ if(CLR_CMAKE_PLATFORM_ARCH_ARM)
     # the include/tdep-arm to include directories
     include_directories(../include/tdep-arm)
 elseif(CLR_CMAKE_PLATFORM_ARCH_ARM64)
-    if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
         # Disable warning due to labs function called on unsigned argument
         add_compile_options(-Wno-absolute-value)
     endif()
diff --git a/src/pal/tests/CMakeLists.txt b/src/pal/tests/CMakeLists.txt
index 5597922f72..0ec630df8c 100644
--- a/src/pal/tests/CMakeLists.txt
+++ b/src/pal/tests/CMakeLists.txt
@@ -32,7 +32,7 @@ endif()
 
 # C++ emits errors and warnings for c-string literal fed into char* parameter
 # this is just to take care of the warnings
-if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   add_compile_options(-Wno-writable-strings)
 elseif (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   add_compile_options(-Wno-write-strings)
diff --git a/src/pal/tests/palsuite/CMakeLists.txt b/src/pal/tests/palsuite/CMakeLists.txt
index 6726165caf..00a4301784 100644
--- a/src/pal/tests/palsuite/CMakeLists.txt
+++ b/src/pal/tests/palsuite/CMakeLists.txt
@@ -14,13 +14,13 @@ endif()
 
 list(APPEND COMMON_TEST_LIBRARIES coreclrpal)
 
-if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   add_compile_options(-Wno-incompatible-pointer-types-discards-qualifiers)
   add_compile_options(-Wno-int-to-void-pointer-cast)
 elseif (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   add_compile_options(-Wno-sign-compare)
   add_compile_options(-Wno-narrowing)
-  SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpermissive" )
+  add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-fpermissive>)
   add_compile_options(-Wno-int-to-pointer-cast)
 endif()