[clang] [Clang] Implement P2280R4 Using unknown pointers and references in constant expressions (PR #95474)

[Konstantin Bogdanov via cfe-commits]

thevar1able wrote:

Hey, I'm seeing a compiler crash after this PR.

https://pastila.nl/?000c2db4/648c000755344e7c43e24c25dd06a571#dyq1EG+tE1OVC+RrCFJoNw==
https://pastila.nl/?ffffffff/32b5c1db56a683e9e5b5b6a8cbed11f7#mDdZiawfthfoxTBwvG8dJg==
https://pastila.nl/?001086ff/212fddaf6ed75f6e0320bd34509c377d#RopRZ8zp/s2UPwcKBzWVXg==

https://github.com/llvm/llvm-project/pull/95474