[Bitcode] Check for live uses of llvm.cmdline/embedded.module

The one use check here is very misleading: At this point we should
actually have no uses, because the only possible use in llvm.used
was already dropped. But because the use in llvm.used is generally
bitcasted, we end up still having one dead use here.

What we actually want to check is that there are no live uses, for
which a helper has recently been added.