Vax and RT compiled with no problems.

Pmax, on paris, I had to compile without AFS support enabled, for two
reasons:

1. There are no AFS libraries and include files in the build tree for
   pmax_ul4.

2. The pmax_ul3 AFS header files conflict with <sys/ioctl.h>, because
   they try to use the old preprocessor method of 'x' and having the x
   substituted in a macro, and that won't work.  The AFS header files
   need to be fixed.

I also had to compile with "ATHLIBDIR=/usr/athena/lib" on the command
line, because the Imake config files seem to think that the libraries
are installed in /usr/local/lib on the pmax, and they're not.  I don't
know if the build will succeed with AFS enabled.

On the rios, on tardis,, I was trying to use the _AIX and AIXV symbols
as the document in /source/control/doc says I should be able to, but
they didn't appear to be working properly.  I settled on _IBMR2, which
does appear to work.  The stuff in /source/control/doc also says that
I should be able to rely on POSIX being set when the compiler is run,
but it doesn't appear to be, so my Imakefile has been modified to set
it explicitly.  If you fix things so that it gets set properly, then
please notify me so that I can remove the hack from my Imakefile.

Once I dealt with the _AIX and AIXV and POSIX problems, everything
compiled fine on the rios.  I had to make some modifications to the
sources to account for the fact that malloc(0) returns 0 on the rios.
Ugh.

I have not tested yet on the Mac because I don't know what machine I'm
supposed to use for testing.  If you come up with a machine that is
prepared to to Mac testing, let me know and I'll deal.  If you end up
deciding to tset on the Mac yourselves, please let me know what
changes (if any) you have to make to the Imakefile or the sources so
that I can incorporate them back into my source tree.