Enable warnings as errors in compiler component on OSX

The commits have addressed all warnings on an OSX build, so to prevent
new warnings from being introduced we enable warnings as errors only on
this platform. Future platforms will follow.

cmake/modules/OmrCompilerSupport.cmake

@@ -283,8 +283,14 @@ function(create_omr_compiler_library)
 	omr_inject_object_modification_targets(COMPILER_OBJECTS ${COMPILER_NAME} ${COMPILER_OBJECTS})
 
 	# warnings as errors and enhanced warnings currently don't work
-	set(OMR_WARNINGS_AS_ERRORS OFF)
-	set(OMR_ENHANCED_WARNINGS OFF)
+	if(OMR_OS_OSX AND OMR_ARCH_X86)
+		set(OMR_WARNINGS_AS_ERRORS ON)
+		set(OMR_ENHANCED_WARNINGS OFF)
+	else()
+		set(OMR_WARNINGS_AS_ERRORS OFF)
+		set(OMR_ENHANCED_WARNINGS OFF)
+	endif()
+
 	set(output_name_args "")
 	if(COMPILER_OUTPUT_NAME)
 		set(output_name_args "OUTPUT_NAME" "${COMPILER_OUTPUT_NAME}")