RTEMS/Ada: Change system configuration

The previous system configuration led to undefined references to
__gnat_raise_nodefer_with_msg().

gcc/ada
	* libgnat/system-rtems.ads (Frontend_Exceptions): Set to False.
	(ZCX_By_Default): Set to True.

From-SVN: r262467

gcc/ada/ChangeLog

+2018-07-06  Sebastian Huber  <sebastian.huber@embedded-brains.de>
+
+	* libgnat/system-rtems.ads (Frontend_Exceptions): Set to False.
+	(ZCX_By_Default): Set to True.
+
 2018-07-02  Martin Liska  <mliska@suse.cz>
 
 	* gnatvsn.ads: Bump Library_Version to 9.

gcc/ada/libgnat/system-rtems.ads

@@ -160,7 +160,7 @@ private
    Always_Compatible_Rep     : constant Boolean := False;
    Suppress_Standard_Library : constant Boolean := False;
    Use_Ada_Main_Program_Name : constant Boolean := False;
-   Frontend_Exceptions       : constant Boolean := True;
-   ZCX_By_Default            : constant Boolean := False;
+   Frontend_Exceptions       : constant Boolean := False;
+   ZCX_By_Default            : constant Boolean := True;
 
 end System;