[clang] [clang] Use getFileLoc when computing getPresumedLoc (PR #166255)

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SergejSalnikov wrote:

> > I'm removing the unnecessary code. The GCDebugInfo used to do `SM.getPresumedLoc(SM.getFileLoc(Loc))` which is now equivalent to `SM.getPresumedLoc(Loc)`
> 
> If that can be done in a separate PR, lets do that

Done

https://github.com/llvm/llvm-project/pull/166255