Fix issue for pointers to anonymous types with -fdump-ada-spec

Fix issue for pointers to anonymous types with -fdump-ada-spec

This used to work long ago but broke at some point.

gcc/c-family/
	* c-ada-spec.cc (dump_ada_import): Deal with the "section" attribute
	(dump_ada_node) <POINTER_TYPE>: Do not modify and pass the name, but
	the referenced type instead.  Deal with the anonymous original type
	of a typedef'ed type.  In the actual access case, follow the chain
	of external subtypes.
	<TYPE_DECL>: Tidy up control flow.