ada: Ignore ghost nodes in call graph information for dispatching calls

ada: Ignore ghost nodes in call graph information for dispatching calls

When emitting call graph information, we already skipped calls to
ignored ghost entities, but this code was causing crashes (in production
builds) and assertion failures (in development builds), because the
ignored ghost entities are not fully decorated, e.g. when they come from
instances of generic units with default subprograms.

With this patch we skip call graph information for ignored ghost
entities when they are registered, both as explicit calls and as
tagged types that will come with internally generated dispatching
subprograms.

gcc/ada/

	* exp_cg.adb (Generate_CG_Output): Remove code for ignored ghost
	entities that applied to subprogram calls.
	(Register_CG_Node): Skip ignored ghost entities, both calls
	and tagged types, when they are registered.