Add old (without --timing) verilator test

test-verilator4/shell.nix

@@ -0,0 +1,19 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+with pkgs;
+let
+  flags-file = "compile_flags.txt";
+in
+mkShell {
+  packages = [ gnumake verilator ];
+
+  shellHook = ''
+    echo -n                                      > ${flags-file}
+    echo -DVM_TRACE=1                           >> ${flags-file}
+    echo -xc++                                  >> ${flags-file}
+    echo -I./testbench                          >> ${flags-file}
+    echo -I${verilator}/share/verilator/include >> ${flags-file}
+    echo -I${clang}/resource-root/include       >> ${flags-file}
+    echo -I${glibc.dev}/include                 >> ${flags-file}
+  '';
+}