[clang] [libcxx] [clang] Add builtin to clear padding bytes (prework for P0528R3) (PR #75371)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

This looks like what I expected; one small comment on the fixes.

https://github.com/llvm/llvm-project/pull/75371