Tests: Add coverage of missing include error.

test_regress/t/t_preproc_inc_notfound_bad.out

@@ -0,0 +1,18 @@
+%Error: t/t_preproc_inc_notfound_bad.v:6: Cannot find include file: this_file_is_not_found.vh
+        ... Looked in:
+             t/this_file_is_not_found.vh
+             t/this_file_is_not_found.vh.v
+             t/this_file_is_not_found.vh.sv
+             obj_dir//this_file_is_not_found.vh
+             obj_dir//this_file_is_not_found.vh.v
+             obj_dir//this_file_is_not_found.vh.sv
+             ../include/this_file_is_not_found.vh
+             ../include/this_file_is_not_found.vh.v
+             ../include/this_file_is_not_found.vh.sv
+             this_file_is_not_found.vh
+             this_file_is_not_found.vh.v
+             this_file_is_not_found.vh.sv
+             obj_vlt/t_preproc_inc_notfound_bad/this_file_is_not_found.vh
+             obj_vlt/t_preproc_inc_notfound_bad/this_file_is_not_found.vh.v
+             obj_vlt/t_preproc_inc_notfound_bad/this_file_is_not_found.vh.sv
+%Error: Exiting due to

test_regress/t/t_preproc_inc_notfound_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(linter => 1);
+
+lint(
+    fails => 1,
+    expect_filename => $Self->{golden_filename},
+    );
+
+ok(1);
+1;

test_regress/t/t_preproc_inc_notfound_bad.v

@@ -0,0 +1,6 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2019 by Wilson Snyder.
+
+`include "this_file_is_not_found.vh"