[clang] Reland "[Modules] Record whether VarDecl initializers contain side effects" (PR #145447)

[Henrik G. Olsson via cfe-commits]

hnrklssn wrote:

> I patched #146468 after this change, rebuilt the compiler and reproduced the same crash. So I guess that patch does not fix the issue I see here. Does #146468 depend on some other change?

It does not. Do you have a reproducer you can share? Does the type that's being casted to `RecordType` have `RecordType` as the canonical type, or is it completely off? Perhaps it could be as simple as replacing `castAs` with `getAs`..?
You don't happen to be using the new constant interpreter?

https://github.com/llvm/llvm-project/pull/145447