Use "rustc" for testing Command args
Use "rustc" for testing Command args

"echo" is not an application on Windows so `Command` tests could fail even if that's not what's being tested for.

aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust