[clang] [clang] Allow class with anonymous union member to be const-default-constructible even if a union member has a default member initializer (#95854) (PR #96301)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

Thank you for this fix. It needs a release note and your summary should have some more details on what the cause of the bug is and how your PR fixes it. efriedma-quic's comment provides a good framework for explaining the cause.

https://github.com/llvm/llvm-project/pull/96301