package/matchbox: forcibly disable support for compositing

package/matchbox: forcibly disable support for compositing

Building with the experimental support for compositing is broken:

    /home/ymorin/dev/buildroot/O/host/usr/bin/arm-linux-gnueabihf-gcc
    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
    -Os -o matchbox-window-manager main.o wm.o base_client.o main_client.o
    toolbar_client.o toolbar_client_alt.o dockbar_client.o dialog_client.o
    select_client.o desktop_client.o ewmh.o misc.o client_common.o keys.o
    list.o stack.o composite-engine.o session.o mbtheme.o xml.o
    -lmb -lX11
    -L/home/ymorin/dev/buildroot/O/host/usr/arm-buildroot-linux-gnueabihf/sysroot/usr/lib
    -lXext -lXcomposite -lXdamage -lXfixes -lXrender
    -L/home/ymorin/dev/buildroot/O/host/usr/arm-buildroot-linux-gnueabihf/sysroot/usr/lib
    -lX11 -lexpat
    -L/home/ymorin/dev/buildroot/O/host/usr/arm-buildroot-linux-gnueabihf/sysroot/usr/lib
    -lXfixes
    composite-engine.o: In function `gaussian':
    /home/ymorin/dev/buildroot/O/build/matchbox-1.2/src/composite-engine.c:65:
    undefined reference to `exp'

That's because it forgets to link with -lm.

However, adding "MATCHBOX_CONF_ENV = -lm" does not solve the issue, as
it still does not link with -lm at all.

Furthermore, the package does not autoreconf, since it is missing the
gconf m4 macros, and Buildroot does not have a package for gconf, hence
we can not even patch Makefile.am and autoreconf.

Patching Makefile.in (in addition to .am) could be a solution, but
support for compositing is explicitly marked as being experimental.

So, just forcibly disable it altogether.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>