DebugInfo: Include enumerators in pubnames

This is consistent with GCC's behavior (which is the defacto standard
for pubnames). Though I find the presence of enumerators from enum
classes to be a bit confusing, possibly a bug on GCC's end (since they
can't be named unqualified, unlike the other names - and names nested in
classes don't go in pubnames, for instance - presumably because one must
name the class first & that's enough to limit the scope of the search)

llvm-svn: 363349