[Ada] Expose part of ownership checking for use in GNATprove

GNATprove needs to be able to call a subset of the ownership legality
rules from marking. This is provided by a new function
Sem_SPARK.Is_Legal.

There is no impact on compilation.

2019-08-14  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* sem_spark.adb, sem_spark.ads (Is_Legal): New function exposed
	for use in GNATprove, to test legality rules not related to
	permissions.
	(Check_Declaration_Legality): Extract the part of
	Check_Declaration that checks rules not related to permissions.
	(Check_Declaration): Call the new Check_Declaration_Legality.
	(Check_Type_Legality): Rename of Check_Type. Introduce
	parameters to force or not checking, and update a flag detecting
	illegalities.
	(Check_Node): Ignore attribute references in statement position.

From-SVN: r274454

gcc/ada/ChangeLog

 2019-08-14  Yannick Moy  <moy@adacore.com>
 
+	* sem_spark.adb, sem_spark.ads (Is_Legal): New function exposed
+	for use in GNATprove, to test legality rules not related to
+	permissions.
+	(Check_Declaration_Legality): Extract the part of
+	Check_Declaration that checks rules not related to permissions.
+	(Check_Declaration): Call the new Check_Declaration_Legality.
+	(Check_Type_Legality): Rename of Check_Type. Introduce
+	parameters to force or not checking, and update a flag detecting
+	illegalities.
+	(Check_Node): Ignore attribute references in statement position.
+
+2019-08-14  Yannick Moy  <moy@adacore.com>
+
 	* sem_spark.adb (Check_Old_Loop_Entry): New procedure to check
 	correct use of Old  and Loop_Entry.
 	(Check_Node): Check subprogram contracts.

gcc/ada/sem_spark.ads

@@ -152,6 +152,12 @@ generic
 
 package Sem_SPARK is
 
+   function Is_Legal (N : Node_Id) return Boolean;
+   --  Test the legality of a node wrt ownership-checking rules. This does not
+   --  check rules related to the validity of permissions associated with paths
+   --  from objects, so that it can be called from GNATprove on code of library
+   --  units analyzed in SPARK_Mode Auto.
+
    procedure Check_Safe_Pointers (N : Node_Id);
    --  The entry point of this package. It analyzes a node and reports errors
    --  when there are violations of ownership rules.