Add very basic example

.gitmodules

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+[submodule "openlibm"]
+	path = openlibm
+	url = https://github.com/redox-os/openlibm.git

openlibm

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+Subproject commit b7b3b4bc31aa4ae42b2562e6adb151e92aa3a82a

unistd/.gitignore

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+/Cargo.lock
+/target/

unistd/Cargo.toml

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+[package]
+name = "unistd"
+version = "0.1.0"
+authors = ["Jeremy Soller <jackpot51@gmail.com>"]
+
+[lib]
+name = "unistd"
+crate-type = ["cdylib"]
+
+[build-dependencies]
+cbindgen = "0.5"
+
+[dependencies]
+libc = "0.2"

unistd/build.rs

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+extern crate cbindgen;
+
+use std::env;
+
+fn main() {
+    let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
+
+    cbindgen::generate(crate_dir)
+      .expect("Unable to generate bindings")
+      .write_to_file("target/unistd.h");
+}

unistd/cbindgen.toml

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+include_guard = "_UNISTD_H"
+language = "C"
+
+[enum]
+prefix_with_name = true

unistd/src/lib.rs

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+/// unistd implementation for Redox, following http://pubs.opengroup.org/onlinepubs/7908799/xsh/unistd.h.html
+
+extern crate libc;
+
+use libc::*;
+
+/*
+#[no_mangle]
+pub extern "C" fn name(arg) -> c_int {
+    unimplemented!();
+}
+*/
+
+#[no_mangle]
+pub extern "C" fn access(pathname: *const c_char, mode: c_int) -> c_int {
+    unimplemented!();
+}
+
+#[no_mangle]
+pub extern "C" fn alarm(seconds: c_uint) -> c_uint {
+    unimplemented!();
+}
+
+#[no_mangle]
+pub extern "C" fn brk(addr: *mut c_void) -> c_int {
+    unimplemented!();
+}
+
+#[no_mangle]
+pub extern "C" fn chdir(path: *const c_char) -> c_int {
+    unimplemented!();
+}
+
+#[no_mangle]
+pub extern "C" fn chroot(path: *const c_char) -> c_int {
+    unimplemented!();
+}
+
+#[no_mangle]
+pub extern "C" fn chown(pathname: *const c_char, owner: uid_t, group: gid_t) -> c_int {
+    unimplemented!();
+}
+
+#[no_mangle]
+pub extern "C" fn close(fd: c_int) -> c_int {
+    unimplemented!();
+}