Add a default-on std feature

.travis.yml

@@ -3,15 +3,19 @@ sudo: required
 dist: trusty
 rust:
   - 1.0.0
+  - stable
   - beta
   - nightly
 services:
   - docker
 script:
   - if [[ $TRAVIS_RUST_VERSION = nightly* ]]; then
       sh ci/run-travis.sh;
+    elif [[ $TRAVIS_RUST_VERSION = "1.0.0" ]]; then
+      cargo build;
     else
       cargo build;
+      cargo build --no-default-features;
     fi
 os:
   - linux

Cargo.toml

@@ -14,4 +14,5 @@ other common platform libraries.
 """
 
 [features]
-default = []
+default = ["use_std"]
+use_std = []

README.md

@@ -24,6 +24,15 @@ Next, add this to your crate root:
 extern crate libc;
 ```
 
+Currently libc by default links to the standard library, but if you would
+instead like to use libc in a `#![no_std]` situation or crate you can request
+this via:
+
+```toml
+[dependencies]
+libc = { version = "0.2", default-features = false }
+```
+
 ## What is libc?
 
 The primary purpose of this crate is to provide all of the definitions necessary

src/lib.rs

@@ -82,7 +82,9 @@
                                reason = "use `libc` from crates.io",
                                issue = "27783"))]
 
-#[cfg(all(not(stdbuild), not(dox)))]
+#![cfg_attr(not(feature = "use_std"), no_std)]
+
+#[cfg(all(not(stdbuild), not(dox), feature = "use_std"))]
 extern crate std as core;
 
 #[macro_use] mod macros;