ada: gnatbind: subprogram spec no longer exists

ada: gnatbind: subprogram spec no longer exists

If a subprogram spec S is present while compiling something that
says "with S;", but the spec is absent while compiling the body
of S, then gnatbind fails to detect the mismatch.  The spec and
body of S might have different parameter and result types.
This patch fixes gnatbind to detect this case and give an error.

gcc/ada/

	* bcheck.adb (Check_Consistency_Of_Sdep): Split out new procedure.
	Add check for special case of subprogram spec that no longer
	exists.
	(Check_Consistency): Call Check_Consistency_Of_Sdep, except when
	Reified_Child_Spec is True. No need for "goto Continue" or "exit
	Sdep_Loop".
	* ali.ads (Subunit_Name, Unit_Name): Change the type to
	Unit_Name_Type. Add a comment pointing to the ALI file
	documentation, because it's in a somewhat-surprising place.
	* ali.adb (Scan_ALI): Subunit_Name and Unit_Name are now
	Unit_Name_Type. Remove comment explaining why Name_Find is used;
	Name_Find is the usual case. Do not remove the "%s" or "%b" from
	the Unit_Name. We need to be able to distinguish specs and bodies.
	This is also necessary to obey the invariant of Unit_Name_Type.
	* binde.adb (Write_Closure): Subunit_Name is now Unit_Name_Type.
	* clean.adb (Clean_Executables): Likewise.