This patch enables the Clang type __vector_pair and its associated LLVM intrinsics even when MMA is disabled. With this patch, the type is now controller by the PPC paired-vector-memops option. The builtins and intrinsics will be renamed to drop the mma prefix in another patch.
Target is a clang::TargetInfo here so there is no HasMMA method available. I'd need to add it, so I guess it's better to use directly hasFeature instead of adding PPC specific code in that class.