Itanium fun

So I've been working on implementing Itanium ABI layout. I've determined that many places in the Wide implementation assumed that every member had an associated LLVM field, which is not true in the presence of the EBCO mandated by Itanium. In addition, I had to implement a few new members and move vptr handling to AggregateType. Previously, there was a bug where since officially, the vptr was a member of the type, then stuff like generated copy assignment operators would copy the vptr (very bad!). Now AggregateType should respect the fact that the vptr is special.

In addition, someone in #llvm pointed out that if I didn't follow Itanium's layout rules, I couldn't use their dynamic_cast implementation, which makes assumptions.

Also, the ClangType implementation of constructor field locations was just totally broken, as well as my handling of EBCO- it was totally non-compliant.

I also had bugs in derived-to-base conversions where a null derived did not lead to a null base. I don't believe I have a single test that actually performs derived-to-base conversions on pointers, although the conversion for references is implemented in those terms.

I also cut down on my overhead by moving some common base-class related functions to Type instead of UserDefinedType and ClangType. There's probably more work I can do in this area, but some functions I'm not comfortable with moving down because they make assumptions about the ABI involved. I know that I don't support any ABI other than Itanium right now, but I'd rather not hardcode that fact into my base-level interface. After all, back when Wide and Clang had diverging ABIs, the basic functionality held together exactly because the Type interface is ABI-independent- except vtable layouts, which currently have their Itanium helper interface coded in the Type interface, which is bad.

I have several Type functions that should probably be static or hell, just non-members. But I'm powering ahead now until exceptions. When I have Itanium ABI exceptions, I'll take a break from new features and clean up/test everything. At least, that's what I promise myself so I can sleep at night. As long as my existing test base passes, it's More Feature Time until I have exceptions.