[Ada] Refine type of Get_Homonym_Number result

Routine Get_Homonym_Number always returns a positive number. This is
explained in its comment and is evident from its body. No test attached,
because semantics is unaffected.

2019-09-18  Piotr Trojanek  <trojanek@adacore.com>

gcc/ada/

	* exp_dbug.ads, exp_dbug.adb (Get_Homonym_Number): Refine type
	from Nat to Pos.
	* sem_util.adb (Add_Homonym_Suffix): Refine type of a local
	variable.

From-SVN: r275851

gcc/ada/ChangeLog

+2019-09-18  Piotr Trojanek  <trojanek@adacore.com>
+
+	* exp_dbug.ads, exp_dbug.adb (Get_Homonym_Number): Refine type
+	from Nat to Pos.
+	* sem_util.adb (Add_Homonym_Suffix): Refine type of a local
+	variable.
+
 2019-09-18  Yannick Moy  <moy@adacore.com>
 
 	* exp_dbug.adb (Append_Homonym_Number): Use new function

gcc/ada/exp_dbug.adb

@@ -1058,9 +1058,9 @@ package body Exp_Dbug is
    -- Get_Homonym_Number --
    ------------------------
 
-   function Get_Homonym_Number (E : Entity_Id) return Nat is
+   function Get_Homonym_Number (E : Entity_Id) return Pos is
       H  : Entity_Id := Homonym (E);
-      Nr : Nat := 1;
+      Nr : Pos := 1;
 
    begin
       while Present (H) loop

gcc/ada/exp_dbug.ads

@@ -460,7 +460,7 @@ package Exp_Dbug is
    -- Subprograms for Handling Qualification --
    --------------------------------------------
 
-   function Get_Homonym_Number (E : Entity_Id) return Nat;
+   function Get_Homonym_Number (E : Entity_Id) return Pos;
    --  Return the homonym number for E, which is its position in the homonym
    --  chain starting at 1. This is exported for use in GNATprove.
 

gcc/ada/sem_util.adb

@@ -26183,7 +26183,7 @@ package body Sem_Util is
 
          if Has_Homonym (U) then
             declare
-               N : constant Nat := Get_Homonym_Number (U);
+               N : constant Pos := Get_Homonym_Number (U);
                S : constant String := N'Img;
             begin
                if N > 1 then