[compiler-rt] [TSan] Clarify and enforce shadow end alignment (PR #144648)

[Kunqiu Chen via llvm-commits]

Camsyn wrote:

Friendly ping @melver. 
Do you have any suggestions for this patch? If not, I will incorporate this PR. 
Anyway, thanks to the reviewers for the detailed review.

https://github.com/llvm/llvm-project/pull/144648