There are several python packages that fail to install on OSx because of C compile problems. When I trying to install virtualenv, I ran into this problem:
clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]
I found http://stackoverflow.com/questions/22313407/clang-error-unknown-argument-mno-fused-madd-python-package-installation-fa helped me get around that issue by add the flags to the compile.
The next issue I had was arround a the ffi library and ffi.h not found. I added to the flags my path to the ffi include directory. Your directory may vary. I ran this to discover the location of the include file:
find / -name ffi.h
The final results for the flags in my ~/.bashrc :
export CFLAGS="-Qunused-arguments -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/include/ffi"
export CPPFLAGS="-Qunused-arguments -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/include/