Fix libc dependency in no_std test

test_suite/no_std/Cargo.toml

@@ -4,5 +4,6 @@ version = "0.0.0"
 publish = false
 
 [dependencies]
+libc = { version = "0.2", default-features = false }
 serde = { path = "../../serde", default-features = false }
 serde_derive = { path = "../../serde_derive" }

test_suite/no_std/src/main.rs

@@ -1,4 +1,4 @@
-#![feature(lang_items, start, libc, compiler_builtins_lib)]
+#![feature(lang_items, start, compiler_builtins_lib)]
 #![no_std]
 
 extern crate libc;