[clang] Consider aggregate bases when checking if an InitListExpr is constant (PR #80519)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

Please be sure to add a release note so users know about the fix, but aside from a bad standards reference, this LGTM (no concerns about C behavior either).

https://github.com/llvm/llvm-project/pull/80519