/proc availability on buildds

[Yavor Doganov <yavor@gnu.org>]

I was unpleasantly surprised to see gnustep-base/1.25.1-2 FTBFS on
GNU/Hurd because of a testsuite failure (NSProcessInfo -systemUptime
returning 0).

The reason for the test failure is this:

| checking kernel support for /proc filesystem... no
| checking support for /proc psinfo struct... no
| checking link to exe of process in /proc... no

1.25.1-1 built successfully on the very same host (mahler) a month ago:

| checking kernel support for /proc filesystem... yes
| checking support for /proc psinfo struct... no
| checking link to exe of process in /proc... /proc/self/exe

Could you please explain what causes this different behavior -- is it
a bug in the gnustep-base package that it assumes /proc is available
on GNU/Hurd?  I'm pretty sure someone (Samuel?) told me long time ago
that it is safe to assume that, for buildd setups specifically.