This started out as trying to remove Bool2int calls, which it does a bit, but
mostly it ended up being removing the Link.Symmorestack array which seemed a
pointless bit of caching.

Change-Id: I91a51eb08cb4b08f3f9f093b575306499267b67a
Reviewed-on: https://go-review.googlesource.com/9239Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>