установка pip: сбой команды clang

Я использую Heroku и использую pip для установки всех требований.txt

Я бегу pip install -r requirements.txt. Он устанавливает кучу пакетов, но затем я получаю

  Running setup.py install for gevent
    building 'gevent.core' extension
    clang -fno-strict-aliasing -fno-common -dynamic -g -Os -pipe -fno-common -fno-strict-aliasing -fwrapv -mno-fused-madd -DENABLE_DTRACE -DMACOSX -DNDEBUG -Wall -Wstrict-prototypes -Wshorten-64-to-32 -DNDEBUG -g -Os -Wall -Wstrict-prototypes -DENABLE_DTRACE -arch i386 -arch x86_64 -pipe -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c gevent/core.c -o build/temp.macosx-10.8-intel-2.7/gevent/core.o
    clang: warning: argument unused during compilation: '-mno-fused-madd'
    In file included from gevent/core.c:253:
    gevent/libevent.h:9:10: fatal error: 'event.h' file not found
    #include "event.h"
             ^
    1 error generated.
    error: command 'clang' failed with exit status 1
    Complete output from command /Users/alexoliveira/Coding/SimplePrints- backend/venv/bin/python -c "import setuptools;__file__='/Users/alexoliveira/Coding/SimplePrints-backend/venv/build/gevent/setup.py';exec(compile(open(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /var/folders/43/yw1jdkb91nqgpnn5lz0ps0wm0000gn/T/pip-dWiY43-record/install-record.txt --single-version-externally-managed --install-headers /Users/alexoliveira/Coding/SimplePrints-backend/venv/include/site/python2.7:
    running install

running build

running build_py

running build_ext

building 'gevent.core' extension

clang -fno-strict-aliasing -fno-common -dynamic -g -Os -pipe -fno-common -fno-strict-aliasing -fwrapv -mno-fused-madd -DENABLE_DTRACE -DMACOSX -DNDEBUG -Wall -Wstrict-prototypes -Wshorten-64-to-32 -DNDEBUG -g -Os -Wall -Wstrict-prototypes -DENABLE_DTRACE -arch i386 -arch x86_64 -pipe -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c gevent/core.c -o build/temp.macosx-10.8-intel-2.7/gevent/core.o

clang: warning: argument unused during compilation: '-mno-fused-madd'

In file included from gevent/core.c:253:

gevent/libevent.h:9:10: fatal error: 'event.h' file not found

#include "event.h"

         ^

1 error generated.

error: command 'clang' failed with exit status 1

Я установил инструменты командной строки Xcode, но это, похоже, не помогает. Я использую Xcode 4.6.1. и Python 2.7.2. Любая помощь могла бы быть полезна.