Fix typos, comments in <pthread.h>

[Mark Kettenis]

   Cc: GNU libc hacker <libc-hacker@sourceware.cygnus.com>
   From: Andreas Jaeger <aj@suse.de>

   OK, here's a patch to not install libc-lock.h.  Looking at dirstream.h
   which seems to be the only header file that uses <bits/libc-lock.h>,
   it seems that it's not installed on any system - there's no need to
   install <bits/libc-lock.h> on any system.  Hurd developers, could you
   double check this, please?.

Wait a moment!  The file `bits/libc-lock.h' is needed to build
libstdc++.  That has always been the reason that we install it.  Of
course there is something wrong here, and we definitely need to clean
things up somehow.  But simply not installing `bits/libc-lock.h' is
not an option.

Mark