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

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huixie90 wrote:

Hi @efriedma-quic I have updated the PR, does this commit https://github.com/llvm/llvm-project/pull/75371/changes/342fe51e090cd9b82edbc188437b4fd77925f2aa
look correct to you?

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