all: fix "Invalid internal option" warning from make

Insert a .WAIT between building of the bootloaders and the CD images,
trying to avoid a build issue as seen on the build cluster:

copying image /home/builds/ab/HEAD/acorn32/201808111340Z-obj/home/source/ab/HEAD/src/distrib/acorn32/ramdisk/ramdisk.fs into netbsd-INSTALL.tmp (2355200 bytes)
done copying image
exiting
rm -f netbsd-INSTALL.gz
cp: /home/builds/ab/HEAD/acorn32/201808111340Z-dest/usr/mdec/boot32,ffa: No such file or directory

branches: 1.19.60; 1.19.62;
Change remaining instances of ${RELEASEDIR}/${MACHINES} to
${RELEASEDIR}/${RELEASEMACHINEDIR}

branches: 1.18.12; 1.18.16;
Add an iso_image target (iso-image as a target name doesn't play well with
bsd.subdirs.mk) in distrib/makefile, which builds an iso image for $MACHINE
with binary sets, stored in ${RELEASEDIR}/iso. The image is bootable for:
alpha, amd64, cats, i386, pmax, sgimips, sparc, sparc64, sun3, vax.
mac68k/macppc no there yet because of missing feature in makefs.

call iso_image in distrib/ for iso-image in the top Makefile.

branches: 1.17.16;
Install release files under "${RELEASEDIR}/${MACHINE}/..." instead of
"${RELEASEDIR}/...".

${RELEASEDIR} is never cleaned , and ${RELEASEDIR}/${MACHINE} is only
cleaned if UPDATE is not defined.

We dont use gzip anymore

branches: 1.15.2;
Switch over to distrib/acorn32/stand/BtNetBSD. Note the created archive is now
BtNetBSD.tar.Z - we don't have zip in tree, and RICS OS SparkPlug
doesn't support tgz. Change discussed with Reinoud.

Use ${.CURDIR} for path to gzip_ff8.bin.uue, so that this would work
with objdirs.

yet another distrib overhaul:
- move guts of distrib/Makefile.inc to distrib/common/Makefile.distrib
(fixes problem caused by implicit include of ../Makefile.inc in certain
submake conditions triggered by makefiles not yet in tree)
- removed mkdir of ${RELEASEDIR}/*; rely upon "snap_pre" target of
etc/Makefile to create all the release directories
- renamed RELINSTALL to RELEASE_INSTALL
- renamed FLOPPYINSTDIR to FLOPPY_RELEASEDIR
- renamed MDSETDIR to MDSET_RELEASEDIR
- removed ITARGET
- move release target from top level to appropriate subdirectory
- ensure release target has correct depends
- replace miniroot's IMAGE_MD_POST with common/Makefile.image IMAGEPOSTBUILD
- Makefile.image: add realall: ${IMAGE}

replace _SRC_TOP_ with NETBSDSRCDIR, since the latter is the "public" version

use gzip -9f

use RELINSTALL from ../Makefile.inc

for consistency reasons, pull in ${_SRC_TOP_}/distrib/Makefile.inc

add .WAIT sync

cleanup and use some more appropriate variables and targets

replace local ${REV} with ${DISTRIBREV} from distrib/Makefile.inc

Make sure <bsd.own.mk> is pulled in before ${PRINTOBJDIR} is used.

Add the RISC OS gzip tool for installation purposes. It gets uudecoded and
installed in ../release/installation/misc/ next to the bootloader.

Oeps... delete a former gzipped tar file first.

Include BtNetBSD in the release !

don't set the owner or group when installing into $RELEASEDIR

Create initial distribution directory for NetBSD/acorn32. There might be
some unused stuff in there like the floppies but i've left them here for
completion. They might be interesting to build one day too.