htl: move symbols into libc

[Samuel Thibault]

Hello,

Concerning the remainder: 

- pt-spin-inlines.c & pt-spin.c should be easy
- pt-get/setname-np.c should be easy
- cancellation.c is probably easy.
- herrno.c can probably just be removed once we have pthread_create
  moved to libc (inet/ already provides _h_errno_location)
- pt-hurd-cond-*.c should be fine to move just like the other
  pthread_cond_* functions
- we probably just want to remove lockfile.c (and thus its forward in
  pthread_functions, thus dropping the forward mechanism at last), so no
  need to work on it.
- similarly, we probably just want to remove cthreads-compat.c

Samuel