Passing target specific command line options to rustc

[Zoxc]

I'm trying to use cargo to build my kernel.

I ran into an issue with cargo rustc not being able to pass along command line arguments to all crates being used for a specific target.

For example I want to pass along --sysroot, -Z no-landing-pads and -C ar to all crates being built with --target, but not compiler plugins.

[Zoxc]

Looks like #2241 will provide a way to do this.

[alexcrichton]

Yes I believe that this is a dupe of #2112, so closing in favor of that.