it's allow you to compile specific defconfig or ARCH or all
as

CROSS_COMPILE=arm-linux- ARCH=arm ./MAKEALL at91sam9263ek_defconfig
CROSS_COMPILE=arm-linux- ARCH=arm ./MAKEALL

The cross-compiler can be specify via
    CROSS_COMPILE               default
    CROSS_COMPILE_<arch>        arch default
    CROSS_COMPILE_<target>      deconfig specifc

it will be evaluated in the invert order

or via config

you can specify it via env CONFIG or option -c (overwrite env)

CONFIG=./MAKEALL.cfg ARCH=arm ./MAKEALL at91sam9263ek_defconfig
CONFIG=./MAKEALL.cfg ARCH=arm ./MAKEALL

and for all

CONFIG=./MAKEALL.cfg ./MAKEALL

you can specify via env or option
env       option
ARCH      -a      arch
CONFIG    -c      config
JOBS      -j      jobs
BUILDDIR  -O      build dir
LOGDIR    -l      log dir

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>