Add --with-wxgtk to use wxGTK and be able to use erlang's graphic tools like observer in Mountain Lion.
Erlang depends on wxWidgets 2.8 API as erlang graphic tools use it. In Mountain Lion WxWidgets 2.8 do not compile
because Carbon has been dropped from XCode 4.4.
To solve this issue WxGTK can be used as it has the same API as WxWidgets 2.8 and use X11 instead of Carbon.
Merge branch 'erlang-wxgtk' of https://github.com/jvalduvieco/homebrew into erlang-wxgtk