link_args attribute should be applicable to crates

[brson]

I frequently write things like

    #[link_args = "-L. -lcairo -lazure"]
    #[nolink]
    native mod m { }

because I need to pass some additional flags to the compiler. I shouldn't need the empty mod.

[Aatch]

#6105 in whatever it's final form ends up being should mitigate this.