libv4l: disable clang

libv4l: disable clang

For the time being, disable clang that is used to build BPF (in-kernel
bytecode machine) protocols.
Indeed, if an old version of clang is found on the host, it could be
used to build object files with a "None" architecture which will be
rejected by support/scripts/check-bin-arch

Fixes:
 - http://autobuild.buildroot.org/results/c18fb7f1ac81496db9c3a4e91ea028a26ca600b0

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>