Windows: autoclose child process if parent dies

[marler8997]

On windows we the weird win32exelink program to forward invocations of zig to the currently configured version. If you kill that process, it doesn't kill the running zig program. We can have the OS do this for us by using a Job (see https://devblogs.microsoft.com/oldnewthing/20131209-00/?p=2433)