[clang] [Clang] Avoid crash when expression requirements are substitution failures (PR #176896)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 commented:

thanks, this needs a release note. PLEASE add an entry to bug fixes to C++ support and link any issues you have fixed. 

https://github.com/llvm/llvm-project/pull/176896