Summary:
Use a set rather than a vector of defined special member functions so
that multiple declarations of the same function are only counted once.
Move some private static member functions into the cpp file.
Run clang-format on header.
Reviewers: ericLemanissier, Prazek, aaron.ballman
Subscribers: Prazek, cfe-commits, nemanjai
Projects: #clang-tools-extra
Differential Revision: https://reviews.llvm.org/D23008
llvm-svn: 277523