Codechange: [OSX] CMake source group for OSX files.

This separates the OSX specific files into a proper folder when generating
Xcode project files.

cmake/MSVCFilters.cmake

@@ -8,6 +8,7 @@ source_group("MD5" REGULAR_EXPRESSION "src/3rdparty/md5/")
 source_group("Misc" REGULAR_EXPRESSION "src/misc/")
 source_group("Music" REGULAR_EXPRESSION "src/music/")
 source_group("Network Core" REGULAR_EXPRESSION "src/network/core/")
+source_group("OSX" REGULAR_EXPRESSION "src/os/macosx/")
 source_group("Pathfinder" REGULAR_EXPRESSION "src/pathfinder/")
 source_group("Save/Load handlers" REGULAR_EXPRESSION "src/saveload/")
 source_group("Sound" REGULAR_EXPRESSION "src/sound/")