Also run "go generate" in
internal/syscall/windows and internal/syscall/windows/registry

Updates #15167

Change-Id: I0109226962f81857fe11d308b869d561ea8ed9f9
Reviewed-on: https://go-review.googlesource.com/23021Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>