[clang] [clang] Add a CodeGen option to ignore compilation directories (PR #149897)

[Steven Wu via cfe-commits]

cachemeifyoucan wrote:

Here is idea to not to add a new option. I am going to remove the fallback in CodeGen but make sure clang-driver does the fallback computation and clang cc1 will always respect that decision from clang-driver. In that case, it is a behavior change for cc1 flag, but not for a driver flag.

https://github.com/llvm/llvm-project/pull/149897