_NETBSD_SOURCE as this makes cross building from older/newer versions of
NetBSD harder, not easier (and also makes the resulting tools 'different')
Wrap all required code with the inclusion of nbtool_config.h, attempt to
only use POSIX code in all places (or when reasonable test w. configure and
provide definitions: ala u_int, etc).
Reviewed by lukem. Tested on FreeBSD 4.9, Redhat Linux ES3, NetBSD 1.6.2 x86
NetBSD current (x86 and amd64) and Solaris 9.
Fixes PR's: PR#17762 PR#25944
round has been tested on Solaris/x86 and Linux hosts.
* Add host tools cap_mkdb, ctags, m4, uudecode.
* Protect __RCSID() and __COPYRIGHT() better.
* Reduce the number of places that need to include "config.h", to keep
sources closer to their "vanilla" versions.
* Add more compat #defines and autoconf-checked functions.
The *_FOREACH macros got added post 1.5 and were pulled up into 1.5.2. This
makes it impossible to compile mtree local on a 1.5-release box as a cross
toolchain bit for bootstrapping to -current. (and why I never saw this problem
on my 1.5.2 machine)
This whole thing is solved via a compat lib for the tools for all netbsd bits
and/or trimming down a version of mtree to just the bits needed for building
the snapshots.
jmc