[clang] [UBSAN][NFC] add coverage for null and alignment checks for aggregates (PR #175023)

[VASU SHARMA via cfe-commits]

vasu-the-sharma wrote:

<img width="1727" height="302" alt="image" src="https://github.com/user-attachments/assets/8f78c6d0-c4c0-48b5-a1bc-34dfab193fdf" />


https://github.com/llvm/llvm-project/pull/175023