[release-branch.go1.16] cmd/compile: mark R16, R17 clobbered for non-standard calls on ARM64

On ARM64, (external) linker generated trampoline may clobber R16
and R17. In CL 183842 we change Duff's devices not to use those
registers. However, this is not enough. The register allocator
also needs to know that these registers may be clobbered in any
calls that don't follow the standard Go calling convention. This
include Duff's devices and the write barrier.

Fixes #46928.
Updates #32773.

Change-Id: Ia52a891d9bbb8515c927617dd53aee5af5bd9aa4
Reviewed-on: https://go-review.googlesource.com/c/go/+/184437


Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Meng Zhuo <mzh@golangcn.org>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Meng Zhuo <mzh@golangcn.org>
(cherry picked from commit 11b4aee0)
Reviewed-on: https://go-review.googlesource.com/c/go/+/331029
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>