[llvm] [BOLT][AArch64] Handle OpNegateRAState to enable optimizing binaries with pac-ret hardening (PR #120064)

[Gergely Bálint via llvm-commits]

bgergely0 wrote:

I've added tests, and created a doc to aid review and for future reference. If it's not something that should be in the patch, I can remove later.

@maksfb you mentioned using a MetaDataRewriter for this on the RFC post, instead of using the two passes. 
I looked into that, and I believe it can work with MarkRAStates becoming the `postCFGInitializer` and InsertNegateRAState becoming the `preEmitFinalizer`.  This will still need a bit of testing, but I marked the PR ready for review, as the contents of that will be the same as the contents of the two passes now.

https://github.com/llvm/llvm-project/pull/120064