Add testcase for incorrect optimization in Ada

gcc/testsuite/
	* gnat.dg/div_zero.adb: New test.

gcc/testsuite/gnat.dg/div_zero.adb

@@ -0,0 +1,23 @@
+-- { dg-do run }
+
+-- This test requires architecture- and OS-specific support code for unwinding
+-- through signal frames (typically located in *-unwind.h) to pass.  Feel free
+-- to disable it if this code hasn't been implemented yet.
+
+procedure Div_Zero is
+
+  pragma Suppress (All_Checks);
+
+  function Zero return Integer is
+  begin
+    return 0;
+  end;
+
+  D : Integer := Zero;
+
+begin
+  D := 1 / D;
+  raise Program_Error;
+exception
+  when Constraint_Error => null;
+end;