[llvm] [BOLT] Add support for safe-icf (PR #116275)

[Amir Ayupov via llvm-commits]

https://github.com/aaupov commented:

Left another round of comments. Will check tests next. Thank you for your patience, it’s a big change.

NB: we have to add ICF-specific processing into scanExternalRefs/disassembly which seems hacky. I think the proper approach would be to have a way to run passes early during disassembly/scanning. Don’t want to make it gating this PR though.

https://github.com/llvm/llvm-project/pull/116275