This makes it possible to report violations of the No_Dependence restriction
during code generation, in other words outside of the Ada front-end proper.
These violations are supposed to be only for child units of System, so the
implementation is restricted to these cases.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* restrict.ads (type ND_Entry): Add System_Child component.
	(Check_Restriction_No_Dependence_On_System): Declare.
	* restrict.adb (Global_Restriction_No_Tasking): Move around.
	(Violation_Of_No_Dependence): New procedure.
	(Check_Restriction_No_Dependence): Call Violation_Of_No_Dependence
	to report a violation.
	(Check_Restriction_No_Dependence_On_System): New procedure.
	(Set_Restriction_No_Dependenc): Set System_Child component if the
	unit is a child of System.
	* snames.ads-tmpl (Name_Arith_64): New package name.
	(Name_Arith_128): Likewise.
	(Name_Memory): Likewise.
	(Name_Stack_Checking): Likewise.
	* fe.h (Check_Restriction_No_Dependence_On_System): Declare.