Thank you for working on it.

This adds an option (USE_CCACHE) to build using ccache if found.

In line with other such options, WITH_COMPILER_CCACHE could be better.

Makefiles, ninja and Xcode are supported.

It is trivial to use ccache with ninja and makefile using :

CMAKE_C_COMPILER_LAUNCHER=ccache
CMAKE_CXX_COMPILER_LAUNCHER=ccache

documented at https://wiki.blender.org/wiki/Building_Blender/Options#Setup_For_Developers and https://cmake.org/cmake/help/latest/prop_tgt/LANG_COMPILER_LAUNCHER.html?highlight=ccache

I'm afraid I have no knowledge of Windows development, so I don't know if this could be made to work with Visual Studio too.

On windows, they use sccache and from what I see in chat, seems to be working fine for people who use it.

As for the approach, it seems long winded and outdated. Since Xcode adds so many more flags to the compiler than Ninja does, there's no point trying to keep the flags same for both generators (to preserve the compiler cache).
I have an initial cache file you can see at F9413084 which allows me to set variables and inject compiler/link flags which I cannot do otherwise without modifying source code.
Only lines 9-12 are enough to make ccache work on Xcode. Please try something similar to that.

EDIT:
One way would be to use execute_process(.. cmake -E create_symlink ccache BUILD_DIRECTORY/ccache_launcher) and then set XCODE..CC to this newly created ccache_launcher and similar for CXX and LD and LDPLUSPLUS

Thanks for taking care of the details!

You can't just link to ccache because it appears CMake's Xcode generator doesn't include the compiler as the first argument.

Oh I see. The commands can be seen in Xcode's build log tab after expanding any compile unit. If it has our custom clang/clang++ as the executable, ccache will work.

Moved everything I can to the platform specific files

The duplicated code for makefiles and Ninja could be in main file too, but don't change it until other reviewers comment.

Final note: I cannot see what's around the changed lines, so create the diff using git diff -U100 or copy it using git diff -U100 | pbcopy

I'll test it on the next update.