test domtree

function %test(i32) {
    block0(v0: i32):
        jump block1     ; dominates: block1
    block1:
        brz v0, block3  ; dominates: block3
        jump block2     ; dominates: block2
    block2:
        jump block3
    block3:
        return
}
; check: cfg_postorder:
; sameln: block2
; sameln: block3
; sameln: block1
; sameln: block0

; check: domtree_preorder {
; nextln: block0: block1
; nextln: block1: block3 block2
; nextln: block3:
; nextln: block2:
; nextln: }