(_hurd_set_brk): Try to allocate more space when we run out.
* sysdeps/generic/sbrk.c: If __curbrk is zero, call __brk with
zero and examine it again.
* sysdeps/unix/sysv/linux/i386/brk.c: New file.
* sysdeps/unix/sysv/linux/i386/brk.S: File removed.
* sysdeps/unix/sysv/linux/i386/sbrk.S: File removed.
* sysdeps/unix/sysv/linux/dl-sysdep.c: New file.