Fixes for building libstd (real)

libstd_real/libc/Cargo.toml

@@ -2,6 +2,7 @@
 name = "libc"
 version = "0.1.0"
 authors = ["Jeremy Soller <jackpot51@gmail.com>"]
+build = "build.rs"
 
 [dependencies]
 redox_syscall = { path = "../../syscall/" }

libstd_real/libc/build.rs

@@ -0,0 +1,18 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![deny(warnings)]
+
+// See comments in Cargo.toml for why this exists
+
+fn main() {
+    println!("cargo:rustc-cfg=stdbuild");
+    println!("cargo:rerun-if-changed=build.rs");
+}

libstd_real/libc/src/lib.rs

@@ -3,6 +3,14 @@
 #![feature(asm)]
 #![feature(naked_functions)]
 
+#![cfg_attr(stdbuild, feature(no_std, core, core_slice_ext, staged_api, custom_attribute, cfg_target_vendor))]
+#![cfg_attr(stdbuild, no_std)]
+#![cfg_attr(stdbuild, staged_api)]
+#![cfg_attr(stdbuild, allow(warnings))]
+#![cfg_attr(stdbuild, unstable(feature = "libc",
+                               reason = "use `libc` from crates.io",
+                               issue = "27783"))]
+
 pub use types::*;
 pub use funcs::*;
 pub use start::*;