[llvm] [TBAA] Assume struct member TBAA does not alias errno (PR #200367)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> ```llvm
> !llvm.errno.tbaa = !{!3}
> !0 = !{!"Simple C/C++ TBAA"}
> !1 = !{!"omnipotent char", !0, i64 0}
> !2 = !{!"int", !1, i64 0}
> !3 = !{!4, !2, i64 0}
> !4 = !{!"errno_struct", !2, i64 0}
> ```

The frontend should be guaranteed to not emit `llvm.errno.tbaa` metadata as a struct-member tag (more at: https://discourse.llvm.org/t/rfc-modelling-errno-memory-effects). I wonder if the Verifier should explicitly reject cases as such.

https://github.com/llvm/llvm-project/pull/200367