stdio locking and Hurd

[Zack Weinberg]

At present there are two implementations of stdio locking:
sysdeps/generic/lockfile.c which doesn't actually lock anything, and
linuxthreads/lockfile.c which winds up in libpthread.  It makes sense to
lock stdio only when libpthread is in use, so we're fine as far as Linux is
concerned.

However, Hurd doesn't use linuxthreads, therefore it has no stdio locking at
all.  Is this an oversight, intentional, or to-fix-later?

zw