instance method build

# File railties/lib/rails/gem_dependency.rb, line 191
    def build(options={})
      require 'rails/gem_builder'
      return if specification.nil?
      if options[:force] || !built?
        return unless File.exists?(unpacked_specification_filename)
        spec = YAML::load_file(unpacked_specification_filename)
        Rails::GemBuilder.new(spec, unpacked_gem_directory).build_extensions
        puts "Built gem: '#{unpacked_gem_directory}'"
      end
      dependencies.each { |dep| dep.build(options) }
    end