[llvm] [BOLT] Fix LLVM_APPEND_VC_REV support (PR #142410)

[Paschalis Mpeis via llvm-commits]

paschalis-mpeis wrote:

Any objections to this PR?

> I will add a validation step on the buildbot to track whether the NFC comparisons are working as expected (ie the commit SHA as well the GNU IDs).

Also, this is implemented by:
- https://github.com/llvm/llvm-zorg/pull/462


https://github.com/llvm/llvm-project/pull/142410