Ctrl+C When Building on Windows Continues Building

I think there's several layers to this one, having to do with child processes and all that jazz.

Issue is if you use `Ctrl+C` to try to end a `e build`, it will keep running, kind of. It will continue any tasks already created for Goma until that runs dry. Since `-j 200` is used with Goma, that means compilation can continue for 10 minutes after you tried to cancel the build.

The behavior if you run the raw `ninja -j 200 electron` command is that `Ctrl+C` ends the build with the message `ninja: build stopped: interrupted by user.`.

Interruption on Windows is really messed up, so there's probably a lot of moving parts to this one.

If you run `e-build.js` directly you get a little closer to it working. I was able to get the desired behavior by adding a `process.on("SIGINT", () => {})` handler, but I have no idea why that worked. I was originally adding it to log to see if it would be called - the log message was never called but the build ended as I wanted. It's almost as if adding that unhooked some other code, but in testing you can add as many `process.on` hooks for `SIGINT` as you want, so I don't know why an empty handler would change the behavior.