syscall: do not pass console handles to PROC_THREAD_ATTRIBUTE_HANDLE_LIST on Windows 7

On Windows 7 (and below), console handles are not real kernel handles
but are rather userspace objects, with information passed via special
bits in the handle itself. That means they can't be passed in
PROC_THREAD_ATTRIBUTE_HANDLE_LIST, even though they can be inherited.
So, we filter the list passed to PROC_THREAD_ATTRIBUTE_HANDLE_LIST to
not have any console handles on Windows 7. At the same time, it turns
out that the presence of a NULL handle in the list is enough to render
PROC_THREAD_ATTRIBUTE_HANDLE_LIST completely useless, so filter these
out too. Console handles also can't be duplicated into parent processes,
as inhertance always happens from the present process, so duplicate
always into the present process even when a parent process is specified.

Fixes #45914.

Change-Id: I70b4ff4874dbf0507d9ec9278f63b9b4dd4f1999
Reviewed-on: https://go-review.googlesource.com/c/go/+/319310


Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>