[clang] [Clang] Provide default value for -fprofile-sample-use, -fprofile-auto (PR #112750)

[Fangrui Song via cfe-commits]

MaskRay wrote:

Actually I think we should drop the accepted and ignored `Flag` form of `-fprofile-sample-use` and `-fprofile-auto`, which is misleading at the least. I have a pending patch, which I will upload at night.

https://github.com/llvm/llvm-project/pull/112750