Properly compute triviality for explicitly-defaulted or deleted special members.

Properly compute triviality for explicitly-defaulted or deleted special members.
Remove pre-standard restriction on explicitly-defaulted copy constructors with
'incorrect' parameter types, and instead just make those special members
non-trivial as the standard requires.

This required making CXXRecordDecl correctly handle classes which have both a
trivial and a non-trivial special member of the same kind.

This also fixes PR13217 by reimplementing DiagnoseNontrivial in terms of the
new triviality computation technology.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169667 91177308-0d34-0410-b5e6-96231b3b80d8