Decouple forward references from optimization

Decouple forward references from optimization

Users who wish to control the level of optimization can
continue to specify -O0, -O1, or -Ox,
where x can be the letter itself, or any number > 1.

However, even with optimization turned off,
NASM will always make enough passes to resolve
forward references. As a result, INCBIN is now the only
item left in the critical expressions list, although TIMES
still has its own constant value check.