Add Libv8::Make module in ext/

This module provides make discovery, it first tries to find gmake and
then falls back to make. This should enable it to work safely and
correctly on both BSD and Linux systems.

ext/libv8/make.rb

@@ -0,0 +1,13 @@
+module Libv8
+  module Make
+    module_function
+
+    def make
+      unless defined?(@make)
+        @make = `which gmake`.chomp
+        @make = `which make`.chomp unless $?.success?
+      end
+      @make
+    end
+  end
+end