[llvm] [llvm] Fix most LLVM_ABI annotations in CAS (PR #203243)

[Nikita Popov via llvm-commits]

https://github.com/nikic approved this pull request.

LGTM

In a followup, it would be good to also replace the LLVM_ABI_FOR_TEST uses in CAS with LLVM_ABI. There should be no LLVM_ABI_FOR_TEST in `include/` headers, only in `lib/` headers. (There are also a few places outside CAS with this issue.)

https://github.com/llvm/llvm-project/pull/203243