Add patch to fix compile errors on OS/X

This patch allows compiling cleanly on OS X 10.9 with newly compiled homebrew libraries, which use clang libc++ instead of gcc's libstdc++. 

If you have upgraded from previous OS X versions and have not recompiled homebrew packages on 10.9, you need to use the old commands. Upgrading to 10.9 without compiling homebrew packages again is not recommended, because it may cause linker errors: for example taglib from old setup with libstdc++ and later compiled vamp-plugins with libc++.

To compile cleanly for mixxx 1.12 with QT 4.x series and current homebrew on OS X 10.9:

scons stdlib=libc++ qtdir=/usr/local/Cellar/qt/HEAD

Also please remember QT 5.x does not currently work with mixxx 1.12 code base.