ada: Improve large unconstrained-but-definite warning

ada: Improve large unconstrained-but-definite warning

Before this patch, Check_Discriminant_Use called Is_Limited type on
entities before they were fully analyzed. That caused Is_Limited_Type
to incorrectly return False for records that are limited because they
have a limited component.

This patch pushes back the emissions of the Check_Discriminant_Use
warning after analysis of record declarations. A new field to
E_Record_Type entity is added to take relevant discriminant uses into
account.

gcc/ada/ChangeLog:

	* gen_il-fields.ads: New field.
	* gen_il-gen-gen_entities.adb: New field.
	* einfo.ads: Document new field.
	* sem_res.adb (Check_Discriminant_Use): Record relevant uses in new
	field. Move warning emission to...
	* sem_ch3.adb (Analyze_Full_Type_Declaration): ... Here.