Areas for Solaris support modernization

I notice that new BF member icarus (OpenIndiana/Illumos)
has been sort of working in recent branches, but when it
gets to trying to run a bunch of test scripts in parallel,
it falls over with errors like

2026-03-01 15:00:29.746 EST [758322] FATAL:  could not create semaphores: No space left on device
2026-03-01 15:00:29.746 EST [758322] DETAIL:  Failed system call was semget(2575969, 17, 03600).

I can reproduce that on a local OpenIndiana image.  Now, we could
tell people they need to increase SEMMNI/SEMMNS, but there's another
answer: unnamed POSIX semaphores seem to work just fine, at least on
recent OpenIndiana.  (And the docs I can find suggest that Solaris
has had them for decades.)  So I think maybe we should add
PREFERRED_SEMAPHORES=UNNAMED_POSIX
as we just did for AIX.

Also, while playing with said local OpenIndiana image, I noticed
that ps_status.c isn't working: "ps auxww" shows all the child
processes with the same command line as the postmaster.  I thought
maybe we'd diked out something important in d2ea2d310, but none
of the code removed there claims to apply to Solaris.  So maybe
it never worked on Solaris?  Anyway, there's room for improvement
there if anyone cares to investigate.

			regards, tom lane