[clang] [CMake] Add a cache file for building a highly-optimized LLVM toolchain (PR #117802)

[Petr Hosek via cfe-commits]

petrhosek wrote:

These cache files seem to be largely the same as [PGO.cmake](https://github.com/llvm/llvm-project/blob/4cec0ba92955c353c52efe728b2cfef3fbdf60f8/clang/cmake/caches/PGO.cmake), [PGO-stage2.cmake](https://github.com/llvm/llvm-project/blob/04b002bbb838bc502bd6d5f602af95efd6cc96b3/clang/cmake/caches/PGO-stage2.cmake), [PGO-stage2-instrumented.cmake](https://github.com/llvm/llvm-project/blob/04b002bbb838bc502bd6d5f602af95efd6cc96b3/clang/cmake/caches/PGO-stage2-instrumented.cmake), the only difference appears to be the inclusion of BOLT. Do we really need separate cache files for that? Could we just extend the existing files?

https://github.com/llvm/llvm-project/pull/117802