Generate nuw GEPs for struct member accesses, as inbounds + non-negative implies nuw. Regression tests are updated using update scripts where possible, and by find + replace where not.
This patch implements P0847R7 (partially), CWG2561 and CWG2653. Reviewed By: aaron.ballman, #clang-language-wg Differential Revision: https://reviews.llvm.org/D140828