Speed up `sort` by special-casing the `value<` ordering

Speed up `sort` by special-casing the `value<` ordering

This gives a 1.5x-2x speed-up when using the default :lessp value,
by eliminating the Ffuncall overhead.

* src/sort.c (order_pred_lisp, order_pred_valuelt): New.
(merge_state, inorder, binarysort, count_run, gallop_left, gallop_right)
(merge_init, merge_lo, merge_hi, tim_sort):
* src/fns.c (Fsort):
When using value<, call it directly.