[llvm] [IR] Do not inherit ABI attributes from the callee (PR #207173)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic commented:

We probably want to add a check to the linter for mismatched ABI.  (As you've noted, it's not necessarily a bug during LTO, but it's an obvious source of problems for anyone writing a frontend.)  And maybe we should consider printing some kind of indicator in textual IR to indicate this is happening.

I think we shouldn't implicitly look through to the callee at all, and instead we should explicitly propagate attributes from the callee to the caller when it's appropriate.  If ABI attributes mismatch, it's not clear what else could be going wrong.  But I guess we could do that as a followup.

https://github.com/llvm/llvm-project/pull/207173