[llvm] r189954 - Revert "Add r159136 back now that pr13124 has been fixed."

[Rafael Espíndola]

> What I'd like is a guarantee that code (incorrectly) relying the presence of
> an implicit instantiation in another TU will not link.

That would be awesome. It would have found pr13124. I don't think we
can fix it in ELF since at that level linkonce_odr and weak_odr look
the same, but we could probably get the IR linker to refuse linking a
declaration to a linkonce_* definition.

I will open a bug with the idea.

Cheers,
Rafael