Add helper c library for posix constants and type sizes.

Rakefile

@@ -10,6 +10,10 @@ Rake::ExtensionTask.new('libpsem') do |ext|
   ext.lib_dir = 'lib/process_shared'
 end
 
+Rake::ExtensionTask.new('helper') do |ext|
+  ext.lib_dir = 'lib/process_shared/posix'
+end
+
 desc 'Run the tests'
 task :default => [:test]
 
@@ -22,3 +26,5 @@ Gem::PackageTask.new(gemspec) do |p|
   p.need_tar = true
   p.gem_spec = gemspec
 end
+
+task :gem => :compile