[Ada] Add sa_messages.ad[sb] for SPARK 2014

These new source files will make it possible to build SPARK 2014 from
a snapshot of GCC FSF sources.

2018-08-21  Pierre-Marie de Rodat  <derodat@adacore.com>

gcc/ada/

	* sa_messages.ads, sa_messages.adb: New source files.

From-SVN: r263706

gcc/ada/ChangeLog

+2018-08-21  Pierre-Marie de Rodat  <derodat@adacore.com>
+
+	* sa_messages.ads, sa_messages.adb: New source files.
+
 2018-08-03  Pierre-Marie de Rodat  <derodat@adacore.com>
 
 	Reverts