c++: Handle ABI for non-polymorphic dynamic classes

c++: Handle ABI for non-polymorphic dynamic classes

The Itanium ABI has specific rules for when virtual tables for dynamic
classes should be emitted.  However we didn't consider structures with
virtual inheritance but no virtual members as dynamic classes for ABI
purposes; this patch fixes this.

gcc/cp/ChangeLog:

	* decl2.cc (import_export_class): Use TYPE_CONTAINS_VPTR_P
	instead of TYPE_POLYMORPHIC_P.
	(import_export_decl): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/virt-5_a.C: New test.
	* g++.dg/modules/virt-5_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>