mxcl/homebrew — pull request #10575 by samueljohn (2012-02-28 23:32:53+00:00)
Title: pixman: Env.x11

pixman uses includes from X11. Declaring Env.x11 makes this explicit (even if it may work on your system without).
Xcode without CLTs needs to set this explicit in order to add the right sdk path.