einfo.ads, einfo.adb (First_Tag_Component): Protect the frontend against errors in the source program...

2006-02-13  Javier Miranda  <miranda@adacore.com>
	    Robert Dewar  <dewar@adacore.com>
	    Ed Schonberg  <schonberg@adacore.com>

	* einfo.ads, einfo.adb (First_Tag_Component): Protect the frontend
	against errors in the source program: a private types for which the
	corresponding full type declaration is missing and pragma CPP_Virtual
	is used.
	(Is_Unchecked_Union): Check flag on Implementation_Base_Type.
	(Is_Known_Null): New flag
	(Has_Pragma_Pure): New flag
	(No_Return): Present in all entities, set only for procedures
	(Is_Limited_Type): A type whose ancestor is an interface is limited if
	explicitly declared limited.
	(DT_Offset_To_Top_Func): New attribute that is present in E_Component
	entities. Only used for component marked Is_Tag. If present it stores
	the Offset_To_Top function used to provide this value in tagged types
	whose ancestor has discriminants.

	* exp_ch2.adb: Update status of new Is_Known_Null flag

	* sem_ch7.adb: Maintain status of new Is_Known_Null flag

	* sem_cat.adb (Get_Categorization): Don't treat function as Pure in
	the categorization sense if Is_Pure was set by pragma Pure_Function.

From-SVN: r111055