[clang] [clang] Don't warn on zero literals with -std=c2y (PR #149688)

[Aaron Ballman via cfe-commits]

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

LGTM, thank you for the fix! (I also like that this fixed some spurious add-on diagnostics.)

https://github.com/llvm/llvm-project/pull/149688