Initial cut at supporting FreeWRT builds under other operating
systems (MirOS BSD, OpenBSD, probably the other BSDs as well;
Mac OSX and Cygwin to come)
The basic idea is:
the old GNU make "Makefile" is renamed to "build.mk"
a wrapper Makefile which uses neither GNU nor BSD make
features calls GNU make with -f build.mk
the wrapper Makefile also checks for prerequisite
tools (as of now: existence of gmake and md5sum)
and their versions (not yet, but that's why it's
being used on GNU/Linux as well)
scripts/md5sum.bsd uses BSD cksum(1) to generate
GNU md5sum compatible output (only when the arguments
are files; no options are supported)
GNU make is symlinked into ./lbin/; md5sum.bsd is
copied there if needed; ./lbin/ is prepended to
$PATH for gmake -f build.mk invocations