[clang] [clang] Add nuw attribute to GEPs (PR #105496)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic approved this pull request.

LGTM; the approach here seems appropriate.

(The EmitCheckedInBoundsGEP API could probably use a refactor so we don't have calls to isSignedOverflowDefined() scattered all over the place, but that's a separate issue.)

https://github.com/llvm/llvm-project/pull/105496