[clang] [UBSAN] [NFC] add coverage for null and alignment checks (PR #176210)

[Justin Stitt via cfe-commits]

JustinStitt wrote:

I just saw https://github.com/llvm/llvm-project/pull/175716. Try to base each new PR on upstream (and not on previous PRs) so that each PR is atomic. See the [Contributing to LLVM - How to Submit a Patch](https://llvm.org/docs/Contributing.html#how-to-submit-a-patch) section about formatting.

https://github.com/llvm/llvm-project/pull/176210