Add VCS and Xcelium run time. Fix RTL for VCS to work correctly

test-vcs/top.sv

@@ -0,0 +1,7 @@
+`timescale 1ps/1ps
+
+module top #(parameter CPU_COUNT = 1024);
+    logic clock = 1'b0;
+    initial forever #(10ns/2) clock = ~clock;
+    testbench #(CPU_COUNT) testbench (clock);
+endmodule