[llvm] [CMake] Simplify building of bolt-optimized clang for distribution builds (PR #117772)

[Tom Stellard via llvm-commits]

tstellar wrote:

As I look into this more, it's not strictly a problem with distribution builds.  Just enabling bolt and running `ninja install-clang` does not give you a bolt optimized clang.  I'm going to try to do a more generic patch.

https://github.com/llvm/llvm-project/pull/117772