[clang-tidy] Ignore empty members and bases in cppcoreguidelines-pro-type-member-init

Summary: Empty/incomplete variables/members/bases don't need to be initialized

Reviewers: mgehre, aaron.ballman, alexfh

Subscribers: nemanjai, cfe-commits

Differential Revision: https://reviews.llvm.org/D25238

llvm-svn: 283886