[Ada] Fix potential Constraint_Error if Library_Version is too long

2018-07-31  Arnaud Charlet  <charlet@adacore.com>

gcc/ada/

	* gnatlink.adb: Fix potential Constraint_Error if
	Library_Version is too long.

From-SVN: r263107

gcc/ada/ChangeLog

 2018-07-31  Arnaud Charlet  <charlet@adacore.com>
 
+	* gnatlink.adb: Fix potential Constraint_Error if
+	Library_Version is too long.
+
+2018-07-31  Arnaud Charlet  <charlet@adacore.com>
+
 	* sem_elab.adb: Remove duplicate condition detected by CodePeer.
 
 2018-07-31  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/gnatlink.adb

@@ -1102,8 +1102,10 @@ procedure Gnatlink is
                   --  We will be looking for the static version of the library
                   --  as it is in the same directory as the shared version.
 
-                  if Next_Line (Nlast - Library_Version'Length + 1 .. Nlast) =
-                       Library_Version
+                  if Nlast >= Library_Version'Length
+                    and then Next_Line
+                      (Nlast - Library_Version'Length + 1 .. Nlast)
+                        = Library_Version
                   then
                      --  Set Last to point to last character before the
                      --  library version.