message: Set Mac OS X deployment target to 10.9
  Without it set, the build will choose the current OS version as the deployment target. 10.9 is the earliest usable, since that is when OS X introduced libc++.
diff: @@ -18,6 +18,7 @@ class OSXBuilder(Builder):
  def getBuildCommand(self, archs, target):
  buildcmd = [
  "xcodebuild",
  + "MACOSX_DEPLOYMENT_TARGET=10.9",
  "ARCHS=%s" % archs[0],
  "-sdk", target.lower(),
  "-configuration", "Release",
  