Merge branch 'use_libc_crate_correctly' into 'master'

Cargo.lock

Cargo.toml

build.rs

posix-regex

src/header/bits_pthread/mod.rs

src/header/grp/mod.rs

src/header/wchar/mod.rs

src/platform/redox/exec.rs

src/platform/redox/libredox.rs

src/platform/redox/mod.rs

src/platform/redox/redox-exec/src/lib.rs

src/platform/redox/signal.rs