[clang] [clang][CodeGen] Use dynamic init for vague-linkage variables without constant initialization (PR #226645)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Currently we have two essentially two forms of "constant": things the C++ standard says are evaluated in a constant context, and things we know evaluate to a specific value using any available information.  (There's a few weird edge cases which don't currently fit this classification, but we're looking at fixing them.)

You're proposing to introduce a third category: things which are constant in the context of a static local.

It's possible to do that, but it only really works if clang and gcc both commit to a stable set of rules.  That means we'd need a complete list of allowed operations.

https://github.com/llvm/llvm-project/pull/226645