hurd: Fix ld.so __access override from libc

ld.so symbols to be overriden by libc need to be extern to really get
overriden. __access happens to have never been exposed, putting it to
GLIBC_PRIVATE.

io/access.c

@@ -39,6 +39,7 @@ __access (const char *file, int type)
   __set_errno (ENOSYS);
   return -1;
 }
+libc_hidden_def (__access)
 stub_warning (access)
 
 weak_alias (__access, access)