Call site cache should be updated when call sites change

[birdstakes]

CONST + CALL pair locations are cached at load time to be used in replace_calls. If an instruction referenced by the cache is modified, the cache should be updated.

Only the original call sites that existed at load time are cached so that new code can call the original unhooked functions without having to worry about a later replace_calls messing things up. Maybe there should also be a way to update the cache to include new call sites too, or an option to have replace_calls skip the cache.