Running 8 building 10 gives "Out of file descriptors" ?

[Dieter BSD]

> I've been building 10.x and 11.x world and kernel from source on an 8.2
> (and more recently now 8.4) system for a couple years, as recently as
> last night.  I've never needed to do anything special.  When I check
> sysctl kern.maxfiles it's set to 12328, not so different from yours.
>
> I wonder if some long-running process on your system is leaking away
> descriptors?  A 'procstat -af' might help find that.

Uptime is less than 3 days.  (System hung a couple days ago, shutting off
the signal to the display.  No core dump.  No clues as to *why* it hung.
*grumble* )

>> getdtablesize() returned 11095

kern.maxfiles: 12328

# procstat -af | wc -l
    1912

I ran
   while true ; do procstat -af | wc -l; sleep 0.03 ; done
in one window, and
   make kernel-toolchain
in another window.  Never got above 2000.  Not absolute proof, but
it looks like it is not really running out of descriptors.

chmod 0 /usr/bin/mkdep
gives the expected permission denied. (proves that it is trying to
run /usr/bin/mkdep)

Restore the mode and change /usr/bin/mkdep to
  #!/bin/sh
  echo hello from mkdep
and I'm back to "Out of file descriptors".  And it doesn't print hello.

So... make (I assume?) thinks (incorrectly?) that it is running out of
file descriptors attempting to run /usr/bin/mkdep?