LowerBitSets: Give names to aliases of unnamed bitset element objects.

LowerBitSets: Give names to aliases of unnamed bitset element objects.

It is valid for globals to be unnamed, but aliases must have a name. To avoid
creating invalid IR, we need to assign names to any aliases we create that
point to unnamed objects that have been moved into combined globals.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239590 91177308-0d34-0410-b5e6-96231b3b80d8