Extend the GlobalObject metadata interface

- Make eraseMetadata return whether it changed something
- Wire getMetadata for a single MDNode efficiently into the attachment
map
- Add hasMetadata, which is less weird than checking getMetadata ==
nullptr on a multimap.

Use it to simplify code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333649 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed