[clang] [compiler-rt] [compiler-rt:ubsan] Add -fsanitize=unaligned-pointer-subtraction to detect undefined subtraction of two pointers (PR #210635)

[Jerry Dang via cfe-commits]

kuroyukiasuna wrote:

> One small comment, otherwise CodeGen changes look fine.
> 
> I'm not really familiar enough with the ubsan runtime to review that side.

Thanks @efriedma-quic ! Who would you recommend as good reviewer to the ubsan runtime side?

https://github.com/llvm/llvm-project/pull/210635