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.

llvm-svn: 201469