stack overflow detection for Windows

Split from #2592

On Windows there are two problems: first, we can't mark a non-committed page as PAGE_GUARD, so we have to pay a cost there (we could let the auto-expand work to ameliorate that). Second, detection of overflow is tied to stack expansion, and the kernel's auto-expansion seems to be based on reservations. When I use -vm_reserve it auto-expands right through whatever (internal) allocation is below the stack, clobbering what's there.