cranelift: rewrite urem of constants

[Kmeakin]

;; x%1 == 0.
;; x%c == x&(c-1) when c is a power of 2.

Note these rules are currently dead, pending resolution of #5908

[cfallin]

These look correct to me; but on further thought, I think we should probably wait to merge until after we have the ability to execute the rule, otherwise we have untested/unfuzzed code waiting to be activated by another, distant infrastructure change. Do you mind if we leave this PR open until after #5908 is resolved somehow?

[Kmeakin]

These look correct to me; but on further thought, I think we should probably wait to merge until after we have the ability to execute the rule, otherwise we have untested/unfuzzed code waiting to be activated by another, distant infrastructure change. Do you mind if we leave this PR open until after #5908 is resolved somehow?

No problem!

[github-actions]

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