Add -Wpedantic to GCC/Clang in CMakeLists

This adds -Wpedantic so we get warned if our code doesn't strictly
conform to ISO C++98. It doesn't seem like MSVC has it.

desktop_version/CMakeLists.txt

@@ -207,7 +207,7 @@ IF(ENABLE_WARNINGS)
 	# Saves quite a few lines and boilerplate at the price of readability.
 	TARGET_COMPILE_OPTIONS(VVVVVV PRIVATE
 		$<$<OR:$<CXX_COMPILER_ID:GNU>,$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>>:
-			-Wall $<$<BOOL:${ENABLE_WERROR}>:-Werror>>
+			-Wall -Wpedantic $<$<BOOL:${ENABLE_WERROR}>:-Werror>>
 		$<$<CXX_COMPILER_ID:MSVC>:
 			/W4 $<$<BOOL:${ENABLE_WERROR}>:/WX>>)
 ENDIF()