[clang] [UBSAN] add null, alignment and array-bounds checks (PR #190739)

[Tony Varghese via cfe-commits]

https://github.com/tonykuttai approved this pull request.

I’m okay with the current changes, except for a few minor nits below. ALso please add a comment explaining why LHS checks are C-only and how this will be covered in a follow up PR as @hubert-reinterpretcast suggested. 

https://github.com/llvm/llvm-project/pull/190739