crucible-mir: Support the exact_div intrinsic

[RyanGlScott]

crucible-mir does not currently support the exact_div family of intrinsics, but it reasonably could. exact_div(x, y) behaves like integer division, except that it produces undefined behavior when x % y != 0 or y == 0 or x == T::MIN && y == -1. Among other uses, this is used in the implementation of array_chunks.