Fix some python version issues with cmake

Summary:
This script will attempt to determine files that will be useful for building with the correct python version.  Currently on macOS with various python installations CMake fails to determine the correct location of python libraries.
Closes facebookarchive/caffe2#163

Reviewed By: Yangqing

Differential Revision: D4594954

Pulled By: bwasti

fbshipit-source-id: c2b750ee9608a02fad4ce2f2293f5fa54dc7011c

Makefile

@@ -1,7 +1,7 @@
 # This makefile does nothing but delegating the actual building to cmake.
 
 all:
-	@mkdir -p build && cd build && cmake .. && make
+	@mkdir -p build && cd build && cmake .. $(python ./scripts/get_python_cmake_flags.py) && make
 
 local:
 	@./scripts/build_local.sh

scripts/get_python_cmake_flags.py

@@ -0,0 +1,39 @@
+##############################################################################
+# Use this script to find your preferred python installation.
+##############################################################################
+#
+# You can use the following to build with your preferred version of python
+# if your installation is not being properly detected by CMake.
+#
+#   mkdir -p build && cd build
+#   cmake $(python ../scripts/get_python_libs.py) ..
+#   make
+#
+
+from __future__ import absolute_import
+from __future__ import unicode_literals
+from __future__ import print_function
+from distutils import sysconfig
+import os
+import sys
+import platform
+
+version = platform.python_version()
+if version[:3] != '2.7':
+    print('ERROR: Python {version} is not officially supported yet.'
+          .format(version=version), file=sys.stderr)
+    exit(1)
+
+# Flags to print to stdout
+flags = ''
+inc = sysconfig.get_python_inc()
+lib = sysconfig.get_config_var("LIBDIR")
+
+# macOS specific
+if sys.platform == "darwin":
+    lib = os.path.dirname(lib) + '/Python'
+    if os.path.isfile(lib):
+        flags += '-DPYTHON_LIBRARY={lib}'.format(lib=lib)
+
+if os.path.isfile(inc + '/Python.h'):
+    flags += '-DPYTHON_INCLUDE_DIR={inc}'.format(inc=inc)