Add regression test for `output reg` syntax for UDPs

Check that it is possible to declare a registered output of a user defined
primitive using the `output reg` syntax.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

ivtest/ivltests/udp_output_reg.v

@@ -0,0 +1,37 @@
+// Check that it is possible to have a `output reg` in a UDP defintion
+
+module test;
+
+  reg clk = 1'b0;
+  reg d = 1'b0;
+  wire q;
+
+  dff ff(q, clk, d);
+
+  initial begin
+    #1
+    clk = 1'b1;
+    #1
+    clk = 1'b0;
+    d = 1'b1;
+
+    if (q === 1'b0) begin
+      $display("PASSED");
+    end else begin
+      $display("FAILED");
+    end
+  end
+
+endmodule
+
+primitive dff(q, c, d);
+  output reg q;
+  input c, d;
+  table
+  //c d : q : q+
+    p 0 : ? : 0 ;
+    p 1 : ? : 1 ;
+    n ? : ? : - ;
+    ? * : ? : - ;
+  endtable
+endprimitive

ivtest/regress-vlg.list

@@ -1667,6 +1667,7 @@ udp_dff			normal			ivltests
 udp_dff_std		normal			ivltests
 udp_eval_arg		normal			ivltests
 udp_jkff		normal			ivltests
+udp_output_reg		normal			ivltests
 udp_real_delay		normal			ivltests
 udp_sched		normal			ivltests
 udp_x			normal			ivltests