[clang] [clang] Implement -Walloc-size diagnostic option (PR #150028)

[Erich Keane via cfe-commits]

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

Yep, you're right about size_t, no idea what I was thinking of.  Also didn't notice this was a 'move'.

https://github.com/llvm/llvm-project/pull/150028