[llvm] [SamplePGO] Support -salvage-stale-profile without probes too (PR #86116)

[via llvm-commits]

WenleiHe wrote:

> There seems to be no good reason to limit this flag to only work for probe-based profiles.

This should help AutoFDO too. We didn't turn it on because we didn't test it throughly for AutoFDO.

Also note that the matching algorithm may not be a no-op for perfectly matched profile. Since we don't have checksum for AutoFDO, we can only apply matching to all functions, which may have undesired side effects for good/matched profiles.  

https://github.com/llvm/llvm-project/pull/86116