When testing with

```
stage4/bin/zig test ../test/behavior.zig -I../test -ofmt=c -target x86_64-windows
```

previously, one would see this message:

```
error: lld-link: subsystem must be defined
```

Now, `--subsystem console` as well as `-lntdll -lkernel32` are on the
`zig run` line, producing a binary.