Don't special case undefined symbol when deciding the symbol order.

Don't special case undefined symbol when deciding the symbol order.

ELF has no restrictions on where undefined symbols go relative to other defined
symbols. In fact, gas just sorts them together. Do the same.

This was there since r111174 probably just because the MachO writer has it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238513 91177308-0d34-0410-b5e6-96231b3b80d8