Fix issues with GCC debugging. GCC emits DWARF in unique ways that LLDB wasn't handli...

Fix issues with GCC debugging. GCC emits DWARF in unique ways that LLDB wasn't handling. This fix will fix cases where classes are forward declared using DW_TAG_structure_type and then actually defined using DW_TAG_class_type. LLDB, when it finds a forward declaration, would try and find and parse the complete type. It does this by:

1 - looking up the type basename in the type index
2 - iterate through all matches and look for decl contexts (namespace/class hierarchy) that match

The issue was the decl context matching wasn't watching for DW_TAG_class_type/DW_TAG_structure_type mismatches, and it wasn't also getting the name for DIE's that didn't have a DW_AT_name, but did have a DW_AT_specification that had a name.

llvm-svn: 186347