DebugInfo: Deduplicate entries in the fission address table

This broke in r185459 while TLS support was being generalized to handle
non-symbol TLS representations.

I thought about/tried having an enum rather than a bool to track the
TLS-ness of the address table entry, but namespaces and naming seemed
more hassle than it was worth for only one caller that needed to specify
this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201469 91177308-0d34-0410-b5e6-96231b3b80d8