Fix testcases that don't pass the verifier after a WIP patch to check
`MDSubprogram` operands more effectively. I found the following issues:
- When `isDefinition: false`, the `variables:` field might point at
`!{i32 786468}`, or at a tuple that pointed at an empty tuple with
the comment "previously: invalid DW_TAG_base_type" (I vaguely recall
adding those comments during an upgrade script). In these cases, I
just dropped the array.
- The `variables:` field might point at something like `!{!{!8}}`,
where `!8` was an `MDLocation`. I removed the extra layer of
indirection.
- Invalid `type:` (not an `MDSubroutineType`).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233466 91177308-0d34-0410-b5e6-96231b3b80d8
