[C2y] Claim conformance to WG14 N3254 (#97581)
The test coverage for this has to lean on LLVM's test coverage for the
actual TBAA behavior, but this demonstrates that Clang emits reasonable
LLVM IR to support this construct. It would be surprising should LLVM
break this pattern given how ubiquitous the pattern is in the wild.
The paper can be found at:
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3254.pdf
