cmake: auto-detect ccache to speed up developer builds (#49389)
Summary:
https://ccache.dev/ is a compiler cache that speeds up subsequent builds. Auto-detecting ccache ensures that it is used on systems where it is available, greatly improving build times for developers. There is no risk in enabling ccache in practice. Please refer to https://ccache.dev/ for a short summary / motivation
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49389
Reviewed By: ejguan
Differential Revision: D27169957
Pulled By: malfet
fbshipit-source-id: 673b60bbceb0d323901c8a992a75792c6da9b805
