Allow unused_imports lint on test where lint only fires on non-linux targets...

Author: pnkfelix

src/test/run-pass/env-null-vars.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![allow(unused_imports)]
+
 // ignore-windows
 // ignore-wasm32-bare no libc to test ffi with