Update build instructions for Solaris 10 hosts

Update build instructions for Solaris 11.3 hosts

Update build instructions for Solaris 11.3 hosts

Update build instructions for Solaris 10 and Solaris 11.3 hosts

Update build instructions for Solaris 11.4 (CBE) hosts

Update build instruction for Solaris 11.4 (CBE) hosts

Update build instructions for Solaris 11.4 hosts: specify HOST_SH and note standards

Update build instruction for Solaris 11.4 hosts

Final note on OpenBSD cross-buildling. Remaining issues were due to
default limits on the build host.

LLVM RT library will actually cross-build from OpenBSD provided sufficient
limits are in place for the build user.

Note OpenBSD cross-build progress

avoid triggering conflict indicator warnings

note on Darwin/Mac

Add macOS High Sierra to the list of verified build platforms

branches: 1.15.2;
More test notes from using build.sh against non NetBSD platforms.

Update with information from recent testing of different Linux variants
on AWS. Also FreeBSD 13.

Add instructions for building NetBSD on modern Solaris 11 hosts

branches: 1.12.82; 1.12.84;
Update notes for testing on linux, OS/X

Note on NetBSD that _NETBSD_SOURCE should never be defined and it's an error
if it is

List that all hosts require a posix sh and override with HOST_SH if needed.
Start a list of any other general tools assumed (gzip being the only one
right now).
Note that redhat8 works with no special settings.

note successful build on Mac OS 10.3 with xcode 1.0 developer tools

It's "HP-UX" not "HP/UX". (Thanks Giles).

preliminary HP/UX notes from Giles; it needs zlib.
(as Solaris, Linux and HP/UX all mention they need zlib and it should
be part of libnbcompat, maybe this is a hint for us to get a move on
and do that :)

Note that RedHat 7.3 hosts successfully as of today with the caveat that
LANG=C must be in the environment.

Update Solaris section (again).

* Always include the NetBSD glob(3) in libnbcompat, as the host
tools use some features of glob(3) that are not available on
all systems.
* Always include the NetBSD vis(3) in libnbcompat, since vis(3)
is not really standardized, and the vis(3) present on some systems
is different from ours.
* Always include the NetBSD MD2, MD4, MD5, RMD160, and SHA1 implementations
in libnbcompat. The host tools use features of the NetBSD versions
which aren't present on all systems that include those functions.
* Add a check for random(3) -- the Heimdal host tools want it.
* Add a check for termios.h -- the Heimdal host tools want it.
* Update the README to indicate the current state of building the
host tools on Solaris 8 (for SPARC).

branches: 1.3.2;
I believe I've fixed nbmake's dependency on /bin/sh.

src/tools/dbsym has been buildable on non-NetBSD systems for some time.

Cross-hosting notes for foreign OS's. (Currently Linux, Solaris, and older
releases of NetBSD.)