[Clang] Implement P2809: Trivial infinite loops are not Undefined Behavior (#90066)

https://wg21.link/P2809R3

This is applied as a DR to C++11 (C++98 did not guarantee forward
progress and is left untouched)

As an extension (and to preserve existing behavior in C), we consider
all controlling expression that can be constant folded
in the front end, not just standard constant expressions.