[clang] [CMake][Release] Build with -ffat-lto-objects (PR #140381)

[Tom Stellard via cfe-commits]

tstellar wrote:

> This is an improvement, but should we also strip the bitcode? Otherwise people will still get errors if they try to use the archives if their host clang version is older.

I think we should strip it.  I've been trying to figure out a way to have cmake do this automatically, but I can't get anything to work.  We may have to add an extra step to the actions workflow to strip the bitcode.

https://github.com/llvm/llvm-project/pull/140381