Most of these checks were already in the `Verifier` so this is more of a
cleanup. Now almost everything is over there.
Now that require a `name:` for `MDGlobalVariable`, add a check in
`LLParser` for it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233657 91177308-0d34-0410-b5e6-96231b3b80d8
