Disallow trivial_abi on a class if all copy and move constructors are

deleted

Instead of forcing the class to be passed in registers, which was what
r350920 did, issue a warning and inform the user that the attribute
cannot be used.

For more background, see this discussion:
http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20190128/259907.html

This fixes PR39683.

rdar://problem/47308221

Differential Revision: https://reviews.llvm.org/D57626