[precompile] Fallback require of ext to prebuilt version.

lib/xcodeproj/project.rb

@@ -1,6 +1,14 @@
 require 'fileutils'
 require 'pathname'
-require 'xcodeproj/xcodeproj_ext'
+
+# In case a binary built for the current Ruby exists, use that, otherwise see
+# if a prebuilt binary exists for the current platform and Ruby version.
+begin
+  require 'xcodeproj/xcodeproj_ext'
+rescue LoadError
+  require "xcodeproj/prebuilt/#{RUBY_PLATFORM}-#{RUBY_VERSION}/xcodeproj_ext"
+end
+
 require 'xcodeproj/project/object'
 require 'xcodeproj/project/project_helper'
 require 'xcodeproj/project/xcproj_helper'