[clang] [clang][CodeGen] Add release note for EmitDeferred re-emission fix (PR #232490)

[Eli Friedman via cfe-commits]

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

> Also answering @efriedma-quic's https://github.com/llvm/llvm-project/pull/223877#discussion_r4286861740

Please don't put this in the commit message.

If there's a corresponding bug report, we usually reference the bug number in the release note.

https://github.com/llvm/llvm-project/pull/232490