[clang] [clang] Implement constexpr heap allocation alignments (PR #174549)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

> I wanted to run this against the clang test suite but I can't merge it on top of main 🤔 Can you rebase this? (and doesn't that need to happen anyway in the end? I'm confused)

I've merged trunk just 40 minutes ago. Did you try before?

https://github.com/llvm/llvm-project/pull/174549