ada: Give a warning for huge imported objects

ada: Give a warning for huge imported objects

This is a follow-up to a recent change, where a warning was implemented
for huge library-level objects.  However it is not given if the objects
are imported, although an indirection is also added for them under the
hood to match the export side.

gcc/ada/ChangeLog:

	* gcc-interface/decl.cc (gnat_to_gnu_entity) <E_Variable>: Give a
	warning for huge imported objects as well.