portability touch-up (and ~15k size-savings)

[Bernhard Fischer]

Hi,

I have introduced one central knob to turn off long options..

   text	   data	    bss	    dec	    hex	filename
 881507	  11420	 646244	1539171	 177c63	busybox_old
 866387	  11196	 645732	1523315	 173e73	busybox.no_getopt_long

This patch is part of my ongoing effort to make busybox a little more
portable (resp. less linux-centric).
Unfortunately the portability diff is getting relatively big
(69962 bytes)..

The patch also introduces a new make target called "hosttools" (see
help-entry in the patch).

As it stands, we're most likely better off to change our policy wrt
platform.h. Forth include "platform.h" in the my-applet.c as the very
first include in order to pull in the proper platform-specific stuff for
your environment. Includes covered by platform.h must not be included
anywhere else.

(see e.g. features.h and the stdint.h/inttypes.h in the patch).