Tracking issue for Windows subsystem support

[alexcrichton]

Tracking issue for rust-lang/rfcs#1665

[yasammez]

Not sure if this is the right place to comment, but since the RFC is already closed, I don't know where else to put it: a future inclusion of the native subsystem would enable us to write Windows kernel mode drivers. And ring 0 is really, where all that safety comes in handy ;-)