So we don't end up with a copy of std::sort in every dialect definition. NFCI.
I guess this is why we should use unique_ptr as much as possible. Also fix the InterfaceAttachmentTest.cpp test. Differential Revision: https://reviews.llvm.org/D110984
LLVM_DEBUG in headers is awkward, better avoid it. DEBUG_TYPE in a header results in a lot of macro redefinition warnings.