ssa: fix defer move block[0] index

cl/_testrt/nextblock/in.go

@@ -0,0 +1,10 @@
+package main
+
+func main() {
+	syms := []int{}
+	for range syms {
+	}
+	defer println("bye")
+	for range syms {
+	}
+}

cl/_testrt/nextblock/out.ll

@@ -0,0 +1 @@
+;

ssa/eh.go

@@ -86,6 +86,7 @@ const (
 func (p Function) deferInitBuilder() (b Builder, next BasicBlock) {
 	b = p.NewBuilder()
 	next = b.setBlockMoveLast(p.blks[0])
+	p.blks[0].last = next.last
 	return
 }