[llvm][NFC] Disallow all warnings in TypeSize tests

This is a follow-up to a request from a reviewer [0]. The text may change in
the future and these tests should not produce any warning output.

[0] https://reviews.llvm.org/D91806#inline-879243

Reviewed By: sdesmalen, david-arm

Differential Revision: https://reviews.llvm.org/D94161