[CIR][CodeGen] Missing handling for global thunk info

[badumbatish]

From #1864 (comment), and #1864 (comment),

Jasmine: CIR crashes at CIRGenVTables.cpp:663, i'm guessing we cannot handle the case where they're different addresses?

Tommy: I remember hitting that when I briefly looked at the issue in the past. Can you create an issue with the test case? ...

Godbolt link: https://godbolt.org/z/cooqvhvqo

Crash at llvm_unreachable in CIRGenVTables.cpp:

void CIRGenVTables::emitThunks(GlobalDecl GD) {
  const CXXMethodDecl *MD =
      cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();

  // We don't need to generate thunks for the base destructor.
  if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
    return;

  const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
      VTContext->getThunkInfo(GD);

  if (!ThunkInfoVector)
    return;

  for ([[maybe_unused]] const ThunkInfo &Thunk : *ThunkInfoVector)
    llvm_unreachable("NYI");
}