Mavericks では ARCHFLAGS を設定してあげないとだめっぽい。

WARNING: '' not a valid package name; please use only.-separated package names in setup.py
--- using frameworks at /System/Library/Frameworks
clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]
clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
error: Setup script exited with error: command 'cc' failed with exit status 1

上記のようなエラーが出るかも。

下記のようにすればOK。

$ brew tap Homebrew/python
$ brew install pillow
$ sudo su -
# export ARCHFLAGS="-Wno-error=unused-command-line-argument-hard-error-in-future"
# easy_install blockdiag