Allow aliases to be unnamed.

Allow aliases to be unnamed.

If globals can be unnamed, there is no reason for aliases to be different.

The restriction was there since the original implementation in r36435. I
can only guess it was there because of the old bison parser for the old
alias syntax.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239921 91177308-0d34-0410-b5e6-96231b3b80d8