The call if_changed mechanism does not work when the command
contains backslashes. This basically is an issue with lzo
and bzip2 compressed kernels. The compressed binaries do not
contain the uncompressed image size, so these use size_append
to append the size. This results in backslashes in the executed
command. With this if_changed always detects a change in the
command and rebuilds the compressed image even if nothing
has changed.

Fix this by escaping backslashes in make-cmd

This was worked out together with Jan Lübbe. The same patch
has recently been accepted to the kernel.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Jan Luebbe <jlu@pengutronix.de>