[Sema] Implement several unary type traits more accurately

is_empty, is_polymorphic, and is_abstract didn't handle incomplete types
correctly.  Only non-union class types must be complete for these
traits.

is_final and is_sealed don't care about the particular spelling of the
FinalAttr.

is_interface_class should always return false regardless of its input.
The type trait can only be satisfied in a mode we do not support (/CLR).

llvm-svn: 253184