[dev.typeparams] runtime/internal/sys: replace uses of GOARCH with goarch.GOARCH

Refactoring performed by the rf tool:

    rf 'ex . {
	import "internal/goarch"
	import "runtime/internal/sys"
	sys.GOARCH -> goarch.GOARCH
    }'

Change-Id: I4b0246bf4e734f08313c6fff7b547db362057714
Reviewed-on: https://go-review.googlesource.com/c/go/+/328338


Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>