syscall: avoid convT2I allocs for common Windows error values

syscall: avoid convT2I allocs for common Windows error values

This is was already done for Unix in https://golang.org/cl/6701 +
https://golang.org/cl/8192. Do it for Windows also.

Fixes #16988

Change-Id: Ia7832b0d0d48566b0cd205652b85130df529592e
Reviewed-on: https://go-review.googlesource.com/28484
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>