Since xfwm-4.2.0-2mdk Xfwm is compiled with compositor support by default.
This is only at compiletime, and it is disabled at runtime in xfce-session
and xfce-utils.

You can choose to enable it at runtime, allthough that's not supported,
because with current Xorg releases the compositor support is still experimental.

If you want to enable compositor at runtime and you have xfce-session
installed (default), the preferred way to change startup behaviour is by
using the "Save session" option in the logout dialog.
If you don't have xfce-session installed, and thus do not use the
session-manager, you can change the xinitrc file of xfce-utils.
You can copy the file /etc/X11/xdg/xfce4/xinitrc to your personal
~/.config/xfce4/ directory and change --compositor=off to --compositor=on,
or just remove that option.

If you want to remove comositor support at compiletime (which shouldn't be
necessary) you can recompile xfwm and use the switch:
$ rpm -ba|--rebuild --without compositor


If you want to read a bit more about Xfwm and the compositor, please
read the COMPOSITOR file in this same Xfwm package.