[release-branch.go1.8] cmd/compile: do not fold large offset on ARM64

Fixes #18933.

Change-Id: I1ab524fdca006100ec6af572065b496f68d6a5c3
Reviewed-on: https://go-review.googlesource.com/36413
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

test/fixedbugs/issue6036.go

-// +build amd64
+// +build !386,!arm,!mips,!mipsle,!amd64p32
 // compile
 
 // Copyright 2013 The Go Authors. All rights reserved.