There are a ton of posts on this subject… with 100 different fixes.
You need Xcode / command line tools / GCC etc. of course.
Most importantly the piece that solved my issue was described here
http://stackoverflow.com/questions/18667916/installing-psycopg2-has-it-stuck-between-xcrun-and-lipo
ln /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/lipo /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/lipo
xcrun -k lipo
Yuji Tomita 