Changed the ABIs and ClangFunction to take a
llvm::ArrayRef of arguments rather than taking
a fixed number of possibly-NULL pointers to
arguments.

Also changed ClangFunction::GetThreadPlanToCallFunction
to take the address of the argument struct by value
instead of by reference, since it doesn't actually
modify the value passed into it.
ObjectiveC migrator. Fixes an obscure bug where
NS_RETURNS_INNER_POINTER ends up unintentionally
on the @property under -objcmt-migrate-all
// rdar://15396636