Log Message:
Mechanically replace all includes of buildlink3.mk of the following
packages with the modular Xorg equivalent. Those are falling back
to the old location by default, so this commmit doesn't change
dependencies.

graphics/xpm ==> x11/libXpm
fonts/Xft2 ==> x11/libXft
x11/Xfixes ==> x11/libXfixes
x11/xcursor ==> x11/libXcursor
x11/Xrender ==> x11/libXrender
x11/Xrandr ==> libXrandr