Added unittest for unsupported arguments

test_regress/t/t_enum_type_methods_bad.out

@@ -0,0 +1,5 @@
+%Error: Internal Error: t/t_enum_type_methods_bad.v:24: ../V3Width.cpp:#: Unsupported: enum next/prev with non-const argument
+                                                      : ... In instance t
+      e.next(increment);
+        ^~~~
+                        ... See the manual and https://verilator.org for more assistance.

test_regress/t/t_enum_type_methods_bad.pl

@@ -0,0 +1,18 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+scenarios(simulator => 1);
+
+compile(
+    fails => 1,
+    expect_filename => $Self->{golden_filename}
+    );
+
+ok(1);
+1;

test_regress/t/t_enum_type_methods_bad.v

@@ -0,0 +1,28 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2014 by Wilson Snyder.
+
+module t (/*AUTOARG*/
+   // Inputs
+   clk,
+   increment
+   );
+   input clk;
+   input [1:0] increment;
+
+   typedef enum [3:0] {
+		       E01 = 1,
+		       E03 = 3,
+		       E04 = 4,
+		       E05 = 5
+		       } my_t;
+
+   my_t e;
+
+   always @ (posedge clk) begin
+      e.next(increment);
+	  $finish;
+   end
+
+endmodule