Consistently use >= operator in both the code and contracts of
function/procedure Overwrite, to facilitate proof, instead of the strict
inequality > sometimes, as only New_Item remains in the result in the
case of equal size too.
gcc/ada/
	* libgnat/a-strbou.ads (Overwrite): Switch to >= operator in
	contracts.
	* libgnat/a-strsup.adb (Super_Overwrite): Switch to >= operator
	in code of procedure (function already uses it).
	* libgnat/a-strsup.ads (Super_Overwrite): Switch to >= operator
	in contracts.
                --  some characters of Source are remaining at the left.
 
                and then
-                 (if New_Item'Length > Max_Length then
+                 (if New_Item'Length >= Max_Length then
 
                     --  New_Item covers all Max_Length characters
 
                --  some characters of Source are remaining at the left.
 
                and then
-                 (if New_Item'Length > Max_Length then
+                 (if New_Item'Length >= Max_Length then
 
                     --  New_Item covers all Max_Length characters
 
 
                  (New_Item (New_Item'First .. New_Item'Last - Droplen));
 
             when Strings.Left =>
-               if New_Item'Length > Max_Length then
+               if New_Item'Length >= Max_Length then
                   Source.Data (1 .. Max_Length) := Super_String_Data
                     (New_Item
                       (New_Item'Last - Max_Length + 1 .. New_Item'Last));
 
             --  Source are remaining at the left.
 
             and then
-              (if New_Item'Length > Source.Max_Length then
+              (if New_Item'Length >= Source.Max_Length then
 
                  --  New_Item covers all Max_Length characters
 
             --  Source are remaining at the left.
 
             and then
-              (if New_Item'Length > Source.Max_Length then
+              (if New_Item'Length >= Source.Max_Length then
 
                  --  New_Item covers all Max_Length characters