test domtree

function %test(i32) {
    ebb0(v0: i32):
        jump ebb1     ; dominates: ebb1
    ebb1:
        brz v0, ebb3  ; dominates: ebb3
        jump ebb2     ; dominates: ebb2
    ebb2:
        jump ebb3
    ebb3:
        return
}
; check: cfg_postorder:
; sameln: ebb2
; sameln: ebb3
; sameln: ebb1
; sameln: ebb0

; check: domtree_preorder {
; nextln: ebb0: ebb1
; nextln: ebb1: ebb3 ebb2
; nextln: ebb3:
; nextln: ebb2:
; nextln: }