This adds functionality to default CROSS_COMPILE to a sensible value
when cross-building (so one doesn't always have to specify this on the
make command line), as well as storing ARCH and SUBARCH in the
Makefile
generated when building outside of the source directory (so that
subsequent make invocations don't have to always repeat these).

From: Jan Beulich <jbeulich@novell.com>

(actual patch attached)