[llvm] [CMAKE][llvm-libraries] Add Precompiled Headers option to improve build times (PR #91755)

[Adrian Prantl via llvm-commits]

adrian-prantl wrote:

My knee-jerk reaction would be: Why don't you just use modules, since we are maintaining a complete module map for the project? Is this an MSVC-specific option?

https://github.com/llvm/llvm-project/pull/91755