AttributeSet::get(... AttributeWithIndex ...) is now private.

AttributeWithIndex is really going away in LLVM 3.3. This is a
horrible hack to keep everything compiling. Attribute handling
needs some rework.
Add ABI infrastructure for PPC64.

The generic ABI works well with PPC64 except for LLVM PR 14779.
(http://llvm.org/bugs/show_bug.cgi?id=14779)
The new ABI infrastucture is based on the UnknownTargetABI. The
PPC64 specific parts coming soon.