[CMAKE] Some options are only supported by GCC, don't use them for clang

These are (so far):
-Wno-format-overflow
-Wno-nonnull-compare
-Wno-old-style-declaration
-Wno-unused-but-set-variable

dll/win32/browseui/CMakeLists.txt

@@ -53,8 +53,11 @@ add_importlibs(browseui uxtheme shlwapi shell32 comctl32 gdi32 ole32 oleaut32 us
 add_pch(browseui precomp.h "${PCH_SKIP_SOURCE}")
 add_cd_file(TARGET browseui DESTINATION reactos/system32 FOR all)
 
+if(CMAKE_C_COMPILER_ID STREQUAL "GNU")
+    target_compile_options(browseui PRIVATE -Wno-unused-but-set-variable)
+endif()
+
 if(NOT MSVC)
-    target_compile_options(browseui PRIVATE "-Wno-unused-but-set-variable")
     # Binutils linker bug
     if(LTCG)
         add_target_link_flags(browseui "-Wl,--allow-multiple-definition")

dll/win32/browseui/shellbars/CMakeLists.txt

@@ -14,8 +14,8 @@ list(APPEND SOURCE
 add_library(shellbars OBJECT ${SOURCE})
 target_link_libraries(shellbars PRIVATE atl_classes)
 
-if(NOT MSVC)
-    target_compile_options(shellbars PRIVATE "-Wno-unused-but-set-variable")
+if(CMAKE_C_COMPILER_ID STREQUAL "GNU")
+    target_compile_options(shellbars PRIVATE -Wno-unused-but-set-variable)
 endif()
 
 add_pch(shellbars shellbars.h SOURCE)

dll/win32/browseui/shellfind/CMakeLists.txt

@@ -11,8 +11,8 @@ list(APPEND SOURCE
 add_library(shellfind OBJECT ${SOURCE})
 target_link_libraries(shellfind PRIVATE atl_classes)
 
-if(NOT MSVC)
-    target_compile_options(shellfind PRIVATE "-Wno-unused-but-set-variable")
+if(CMAKE_C_COMPILER_ID STREQUAL "GNU")
+    target_compile_options(shellfind PRIVATE -Wno-unused-but-set-variable)
 endif()
 
 add_pch(shellfind shellfind.h SOURCE)

dll/win32/winmm/CMakeLists.txt

@@ -33,8 +33,8 @@ add_importlibs(winmm advapi32 user32 msvcrt kernel32 ntdll)
 add_pch(winmm winemm.h SOURCE)
 add_cd_file(TARGET winmm DESTINATION reactos/system32 FOR all)
 
-if(NOT MSVC)
-    target_compile_options(winmm PRIVATE "-Wno-unused-but-set-variable")
+if(CMAKE_C_COMPILER_ID STREQUAL "GNU")
+    target_compile_options(winmm PRIVATE -Wno-unused-but-set-variable)
 endif()
 
 add_subdirectory(midimap)