Fixes for building libstd (real)

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");
+}