Make rake gem vendor libre2 and abseil tarballs

This increases the size of the gem from 32K to 2.4 MB, but this will
significantly reduce network transfer and avoid rate limits.

Rakefile

@@ -12,10 +12,44 @@ CLOBBER.include FileList['**/tmp'],
                 FileList['tmp/']
 CLOBBER.add("ports/*").exclude(%r{ports/archives$})
 
+RE2_GEM_SPEC = Gem::Specification.load('re2.gemspec')
+
 Rake::ExtensionTask.new('re2')
 
+Gem::PackageTask.new(RE2_GEM_SPEC) do |p|
+  p.need_zip = false
+  p.need_tar = false
+end
+
 RSpec::Core::RakeTask.new(:spec)
 
+def gem_build_path
+  File.join 'pkg', RE2_GEM_SPEC.full_name
+end
+
+def add_file_to_gem(relative_source_path)
+  dest_path = File.join(gem_build_path, relative_source_path)
+  dest_dir = File.dirname(dest_path)
+
+  mkdir_p dest_dir unless Dir.exist?(dest_dir)
+  rm_f dest_path if File.exist?(dest_path)
+  safe_ln relative_source_path, dest_path
+
+  RE2_GEM_SPEC.files << relative_source_path
+end
+
+def add_vendored_libraries
+  dependencies = YAML.load_file(File.join(File.dirname(__FILE__), 'dependencies.yml'))
+  abseil_archive = File.join('ports', 'archives', "#{dependencies['abseil']['version']}.tar.gz")
+  libre2_archive = File.join('ports', 'archives', "re2-#{dependencies['libre2']['version']}.tar.gz")
+
+  add_file_to_gem(abseil_archive)
+  add_file_to_gem(libre2_archive)
+end
+
+task gem_build_path do
+  add_vendored_libraries
+end
+
 task :spec    => :compile
 task :default => :spec
-