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

[via llvm-commits]

h-vetinari wrote:

> Please wait a couple of days if folks more familiar with VC_REV functionality want to chime in:

Did you intend to ping me? I'm not familiar with that. 👀 

In fact, I first completely misinterpreted this as refering to VC the MSVC toolchain (and wondering whether bolt started supporting windows), but it seems VC is version control:
https://github.com/llvm/llvm-project/blob/6c1091ea3fb7ab31aa9b8406cb32b9a549c4e7cd/llvm/cmake/modules/AddLLVM.cmake#L2593-L2600

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