cmd/go: encode backslash and newline in response files

Fixes #42295

Change-Id: Ie324bc99a74c1d864c6c2da2e7b929b338c2e033
Reviewed-on: https://go-review.googlesource.com/c/go/+/272870


Trust: Jeremy Faller <jeremy@golang.org>
Run-TryBot: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>