Check before using -mno-ms-bitfields

src/CMakeLists.txt

@@ -408,8 +408,8 @@ endif()
 # Compatibility flag with later versions of GCC
 # We should really fix our code to not need this
 if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
-	check_cxx_compiler_flag("-mno-ms-bitfields" HAS_MS_BITFIELDS)
-	if(HAS_MS_BITFIELDS)
+	check_cxx_compiler_flag("-mno-ms-bitfields" HAS_NO_MS_BITFIELDS)
+	if(HAS_NO_MS_BITFIELDS)
 		target_compile_options(SRB2SDL2 PRIVATE -mno-ms-bitfields)
 	endif()
 endif()