Fix an undefined behavior in fortran/decl.c

From-SVN: r255332

gcc/fortran/ChangeLog

+2017-12-01  Qing Zhao  <qing.zhao@oracle.com>
+
+	* decl.c (gfc_get_pdt_instance): Adjust the call to sprintf
+	to avoid the same buffer being both source and destination.
+
 2017-12-01  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	PR fortran/83224

gcc/fortran/decl.c

@@ -3362,7 +3362,7 @@ gfc_get_pdt_instance (gfc_actual_arglist *param_list, gfc_symbol **sym,
 	}
 
       gfc_extract_int (kind_expr, &kind_value);
-      sprintf (name, "%s_%d", name, kind_value);
+      sprintf (name + strlen (name), "_%d", kind_value);
 
       if (!name_seen && actual_param)
 	actual_param = actual_param->next;