[cmake] workaround for older GCC

To fix the missing pragma -Wunknown-pragmas support for older GCC
disable this warning altogether if such a compiler is detected

Author: akallabeth

cmake/CXXCompilerFlags.cmake

@@ -74,5 +74,10 @@ if (WIN32)
     add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-DNOMINMAX>)
 endif()
 
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53431
+if (CMAKE_COMPILER_IS_GNUCC AND (CMAKE_CXX_COMPILER_VERSION LESS 13))
+	CheckCFlag(-Wno-unknown-pragmas)
+endif()
+
 set(CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS} CACHE STRING "default CXXFLAGS")
 message("Using CXXFLAGS ${CMAKE_CXX_FLAGS}")

cmake/CompilerFlags.cmake

@@ -57,6 +57,11 @@ if (ENABLE_WARNING_ERROR)
 	CheckCFlag(-Werror)
 endif()
 
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53431
+if (CMAKE_COMPILER_IS_GNUCC AND (CMAKE_C_COMPILER_VERSION LESS 13))
+	CheckCFlag(-Wno-unknown-pragmas)
+endif()
+
 CheckCFlag(-fno-omit-frame-pointer)
 
 CheckCFlag(-fmacro-prefix-map="${CMAKE_SOURCE_DIR}"="./")