[Clang][CodeGen] Follow-up for `vtable`, `typeinfo` et al. are globals

https://reviews.llvm.org/rG8acdcf4016876d122733991561be706b64026e73 didn't include handling for the fact that `throw`'s implementation takes a pointer to a type's `typeinfo` struct, which implies that its signature needs to change as well. This corrects that and adds a test.

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D155759