[Ada] System.Strings.Stream_Ops: do not depend on Stream_IO

[Pierre-Marie de Rodat]

Dependence was only from Ada.Streams.Stream_IO.End_Error exception which
is renaming of the Ada.IO_Exceptions.End_Error. Use
Ada.IO_Exceptions.End_Error directly.

Tested on x86_64-pc-linux-gnu, committed on trunk

2019-07-10  Dmitriy Anisimkov  <anisi...@adacore.com>

gcc/ada/

        * libgnat/s-ststop.adb: Remove System.Strings.Stream_Ops
        dependence on System.Streams.Stream_IO.
--- gcc/ada/libgnat/s-ststop.adb
+++ gcc/ada/libgnat/s-ststop.adb
@@ -31,8 +31,8 @@
 
 pragma Compiler_Unit_Warning;
 
+with Ada.IO_Exceptions;        use Ada.IO_Exceptions;
 with Ada.Streams;              use Ada.Streams;
-with Ada.Streams.Stream_IO;    use Ada.Streams.Stream_IO;
 with Ada.Unchecked_Conversion;
 
 with System;                   use System;