Fix platform

- Add cfg to extern crate sc. It is not used by redox.
 - Fix bad syntax in brk implementation for redox
 - nits
   - style: update brk implementation for linux
   - style: no space between not operator and ptr.is_null
   - style: should be a space around = in module path

platform/src/lib.rs

@@ -3,6 +3,7 @@
 #![no_std]
 #![allow(non_camel_case_types)]
 
+#[cfg(all(not(feature="no_std"), target_os = "linux"))]
 #[macro_use]
 extern crate sc;