[llvm] [IR] Fix undiagnosed cases of structs containing scalable vectors (PR #113455)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Thanks for the fix! Just curious about what kind of test would fail?

The last two cases that I added to `test/Verifier/scalable-global-vars.ll` would fail without this fix.

https://github.com/llvm/llvm-project/pull/113455