squashfs used the get_nprocs() GNU extension, instead of directly
calling sysconf(), breaking the build on uClibc.
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Pass CFLAGS and LDFLAGS so that when building squashfs, it finds the
zlib installed in $(HOST_DIR).
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>