[clang] Fix crash with modules and constexpr destructor (PR #69076)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

> While the change itself looks neat, I am curious about the reason how this interact with modules.

IIUC modules is incidental to the problem, it is just a way we run into an underlying issue that we are not dealing with full-expressions properly in this case.

https://github.com/llvm/llvm-project/pull/69076