[compiler-rt] [compiler-rt][ARM] Add missing PACBTI support to assembly aeabi functions (PR #142400)

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

If I've understood the rtabi correctly I think we're not allowed to corrupt r0 in the 3-way comparison routines, which it looks like we're doing in a couple of cases.

The rest looks good to me. There could be a case for adding some closing comments to the #else and #endif as nested ones can be awkward to figure out. Although in this case they are always the innermost ones.

The other possibility I thought about was to have a macro that conditionally expanded to `, r12` or nothing depending on whether PAC was being used. That could be used in the save list for push, however I don't think there's any precedent for that in compiler-rt so it's probably not a good idea. 

https://github.com/llvm/llvm-project/pull/142400