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

[Mikołaj Piróg via cfe-commits]

mikolaj-pirog 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.
> 
> For sample PGO, the profile file extension is usually `.afdo`, but I don't think it makes sense to have a default filename.

I think this isn't the best solution, since it is inconsistent with the behavior of the `-fprofile-use` option. Why should `-fprofile-use` be accepted and `-fprofile-sample-use` rejected? TBH I think the whole looking for default filename isn't the best option, but to make things consistent it seems to easier to introduce this behavior for `-fprofile-sample/auto-use` rather than take it from `-fprofile-use`


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