os: fix hex exit code print on 32-bit windows
os: fix hex exit code print on 32-bit windows

We want to print hex exit codes for the large values,
but on 32-bit Windows the large values are negative.

Change-Id: I0e350b128414a9468c93eddc62d660f552c1ee05
Reviewed-on: https://go-review.googlesource.com/c/go/+/294070
Trust: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

golang/go,nawawi/go,cloudflare/go,cloudflare/go,golang/go,nawawi/go,golang/go,CAFxX/go,nawawi/go,cloudflare/go,nawawi/go,cloudflare/go,golang/go,golang/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,CAFxX/go,CAFxX/go,cloudflare/go,golang/go,nawawi/go,CAFxX/go,golang/go,CAFxX/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,nawawi/go