[clang] [clang] Strict aliasing warning ala GCC [PR50066] (PR #74155)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Making Sema pull the TBAA info out of clang/lib/CodeGen is a layering violation (and probably breaks if we aren't actually generating code).  If we need some notion of "aliasing" in Sema, we should pull the relevant code into clang/lib/AST.

I don't have any experience with this warning, so I'm not sure how effective it is at detecting issues; do a significant fraction of issues actually show up at a pure syntactic level?  Do you have any idea what false positive rate we should expect?

https://github.com/llvm/llvm-project/pull/74155