[clang] [clang] Support constexpr alignment of __builtin_assume_aligned. (PR #127223)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

This is not the right fix.

After we check the constant expression in Sema, we should create a ConstantExpr containing the the evaluated value, so we don't need to re-evaluate it later.

https://github.com/llvm/llvm-project/pull/127223