It was working like a charm before the update from Mountain Lion.
After the update it is broken and I cannot get the environment up again.
Does anybody know
The problem is due to changes introduced in Xcode 5.1 and due to the way the Apple-supplied system Python 2.7 is built. Try adding these environment variable values before running pip:
export CFLAGS=-Qunused-arguments
export CPPFLAGS=-Qunused-arguments
See clang error: unknown argument: '-mno-fused-madd' (python package installation failure) for more information.
UPDATE [2014-05-16]: As expected, Apple has fixed this problem with updated system Pythons (2.7, 2.6, and 2.5) in OS X 10.9.3 so the workaround is no longer necessary when using the latest Mavericks and Xcode 5.1+. However, as of now, the workaround is still required for OS X 10.8.x (Mountain Lion, currently 10.8.5) if you are using Xcode 5.1+ there.