Regression test that optional for_step works

Add the br_gh801b.v regression test.

ivtest/ivltests/br_gh801b.v

@@ -0,0 +1,21 @@
+
+module main;
+   initial begin
+      int idx;
+      for (idx = 1 ; idx < 5 ; ) begin
+	 $display("... %02d", idx);
+	 idx += 1;
+      end
+      if (idx !== 5) begin
+	 $display("FAILED -- idx=%0d", idx);
+	 $finish;
+      end
+      idx = 2;
+      for ( ; idx < 5 ; ) begin
+	 $display("... %02d", idx);
+	 idx += 1;
+      end
+      $display("PASSED");
+      $finish;
+   end
+endmodule // main

ivtest/regress-sv.list

@@ -222,6 +222,7 @@ br_gh699		CE,-g2009		ivltests
 br_gh756		normal,-g2009		ivltests
 br_gh782a		normal,-g2009		ivltests gold=br_gh782a.gold
 br_gh801		normal,-g2009		ivltests
+br_gh801b		normal,-g2009		ivltests
 br_ml20171017		normal,-g2009		ivltests
 br_ml20180227		CE,-g2009		ivltests
 br_ml20180309a		normal,-g2009		ivltests