[clang] [flang] [llvm] [mlir] [polly] [CMake][LLVM] Add PCH infrastructure and LLVMSupport PCH (PR #176420)

[Renato Golin via cfe-commits]

rengolin wrote:

> @rengolin This particular error should also be fixed by #182850. Any other error logs you can share?

Nope, those were the ones we've seen. @shahidact can you check if this helps?

https://github.com/llvm/llvm-project/pull/176420