[clang] [clang][CodeGen] Zero init unspecified fields in initializers in C (PR #97121)

[Eli Friedman via cfe-commits]

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

LGTM

I think we'll need to watch out for performance regressions... in most cases, we can probably zero-pad cheaply, but there might be cases where it isn't cheap, or cases where it should be cheap but the LLVM backend can't figure it out.  There's a limit to how much we can do before this lands... but maybe helpful if you can show Linux kernel codesize as a reference, to show there aren't massive issues.

https://github.com/llvm/llvm-project/pull/97121