[clang] [Clang] Fix crash in alignment builtins with null pointers (PR #224549)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

(Even if we don't do the folding in constant evaluation, the value will just get immediately folded as soon as we get to LLVM IR anyway.)

https://github.com/llvm/llvm-project/pull/224549