Handle gcc 4.8.1's DWARF output

[anevilyak]

Along with its switch over to DWARF 4 by default, gcc 4.8.1 has started generating info entries corresponding to rvalue reference types, which we don't currently handle. This needs to be addressed.

Furthermore, it seems it's generating DWARF 4 output without generating a separate debug_types section, which the current implementation did not anticipate. Needs further investigation.

[anevilyak]

As of hrev46697, handling of gcc4.8's DWARF4 output is functioning again. However, an issue of some form remains when using -fdebug-types-section, the info for complex types such as classes doesn't seem to be getting resolved correctly in some way. Will investigate as time permits, since this was working with 4.7.

[anevilyak]

Fixed .debug_types handling in hrev46998. Hypothetically our gcc could still be configured to pass -fdebug-types-section by default, but that isn't a hurdle for this ticket.