If a long branch doesn't use delay slot, then when optimizing it
to a regular branch, the instruction in delay slot should be set
to nop.

Change-Id: Id3015bc0c562725258705a8bc6647c4011d96c2a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2524416Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#71039}