[Ada] Avoid confusing warning on exception propagation in GNATprove mode

When compiling with the restriction No_Exception_Propagation, GNAT compiler
may issue a warning about exceptions not being propagated. This warning is
useless and confusing to users for GNATprove analysis, as GNATprove
precisely detects possible exceptions, so disable the warning in that mode.

2018-07-17  Yannick Moy  <moy@adacore.com>

gcc/ada/

	* gnat1drv.adb (Gnat1drv): Do not issue warning about exception not
	being propagated in GNATprove mode.

From-SVN: r262781

gcc/ada/ChangeLog

+2018-07-17  Yannick Moy  <moy@adacore.com>
+
+	* gnat1drv.adb (Gnat1drv): Do not issue warning about exception not
+	being propagated in GNATprove mode.
+
 2018-07-17  Dmitriy Anisimkov  <anisimko@adacore.com>
 
 	* libgnat/g-socket.adb, libgnat/g-socket.ads: Reorganize and make

gcc/ada/gnat1drv.adb

@@ -467,6 +467,12 @@ procedure Gnat1drv is
 
          Ineffective_Inline_Warnings := True;
 
+         --  Do not issue warnings for possible propagation of exception.
+         --  GNATprove already issues messages about possible exceptions.
+
+         No_Warn_On_Non_Local_Exception := True;
+         Warn_On_Non_Local_Exception := False;
+
          --  Disable front-end optimizations, to keep the tree as close to the
          --  source code as possible, and also to avoid inconsistencies between
          --  trees when using different optimization switches.