Fix locating stdlib on macos

When compiling on mac with xcode 10 the standard library headers are not found.
This adds an extra compile and link option to find them.

setup.py

@@ -26,7 +26,7 @@
 import distutils.ccompiler
 from distutils.dep_util import newer
 from distutils.command.install import install as _install
-import sys, glob, os, fnmatch
+import sys, glob, os, fnmatch, platform
 import subprocess
 import shlex
 
@@ -35,6 +35,7 @@
 from fofix.core import Version, SceneFactory
 
 from setuptools import setup, Extension, Command
+import pkg_resources
 from Cython.Build import cythonize
 
 
@@ -462,11 +463,20 @@ def run(self):
 else:
     vidInclude = ['.']
 
+extra_compile_args_pitch = [];
+extra_link_args_pitch = [];
+if os.uname()[0] == "Darwin" and pkg_resources.parse_version(os.uname()[2]) >= pkg_resources.parse_version("17.7.0"):
+  print("success")
+  extra_compile_args_pitch.append("-stdlib=libc++")
+  extra_link_args_pitch.append("-stdlib=libc++")
+
 extensions = [
     Extension('fofix.lib.cmgl', ['fofix/core/cmgl/cmgl.pyx'], **combine_info(numpy_info, gl_info)),
     Extension('fofix.lib._pypitch',
               language='c++',
-              sources=['fofix/core/pypitch/_pypitch.pyx', 'fofix/core/pypitch/pitch.cpp']),
+              sources=['fofix/core/pypitch/_pypitch.pyx', 'fofix/core/pypitch/pitch.cpp'],
+              extra_compile_args=extra_compile_args_pitch,
+              extra_link_args=extra_link_args_pitch),
     Extension('fofix.lib._VideoPlayer',
               ['fofix/core/VideoPlayer/_VideoPlayer.pyx', 'fofix/core/VideoPlayer/VideoPlayer.c'],
               **combine_info(gl_info, ogg_info, theoradec_info, glib_info, swscale_info,