fix tests

test_regress/t/t_split_var_1_bad.v

@@ -37,4 +37,3 @@ module sub2(input [3:0]addr, output logic [7:0] rd_data);
         rd_data = cannot_split[addr];
 
 endmodule
-

test_regress/t/t_split_var_2_trace.pl

@@ -10,8 +10,11 @@ if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); di
 scenarios(simulator => 1);
 top_filename("t/t_split_var_0.v");
 
+# Travis environment offers 2 VCPUs, 2 thread setting causes the following warning.
+# %Warning-UNOPTTHREADS: Thread scheduler is unable to provide requested parallelism; consider asking for fewer threads.
+# So use 4 threads here though it's not optimal in performace wise, but ok.
 compile(
-    verilator_flags2 => ['--cc --trace'],
+    verilator_flags2 => [$Self->{vltmt} ? '--cc --trace --threads 4' : '--cc --trace ' ],
     );
 
 execute(