runtime/cgo: use CreateThread instead of _beginthread
_beginthread is intended to be used together with the C runtime.
The cgo runtime doesn't use it, so better use CreateThread directly,
which is the Windows API for creating threads.
Cq-Include-Trybots: luci.golang.try:gotip-windows-amd64-longtest,gotip-windows-arm64
Change-Id: Ic6cf75f69f62a3babf5e74155da1aac70961886c
Reviewed-on: https://go-review.googlesource.com/c/go/+/651995 Reviewed-by: Michael Pratt <mpratt@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>