AsmParser: Make the code for parsing unnamed aliases more closely resemble that for unnamed globals.

This fixes parsing of forward references to unnamed aliases.

While here, remove an unnecessary isa check.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254054 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed