[clang] [coverage] fix crash in code coverage and `if constexpr` with `ExprWithCleanups` (PR #80292)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> > Changes LGTM, but please add a release note to `clang/docs/ReleaseNotes.rst` so users know about the fix.
> > Thank you for the fix!
> 
> FYI this is a regression in 18 affecting users so we should backport

Btw, instructions on how to do that can be found here: https://www.llvm.org/docs/GitHub.html#backporting-fixes-to-the-release-branches

https://github.com/llvm/llvm-project/pull/80292