Merge branch 'master' into 'master'

include/bits/unistd.h

src/c/unistd.c

src/platform/Cargo.toml

src/platform/src/lib.rs

src/platform/src/redox/mod.rs

src/unistd/cbindgen.toml

src/unistd/src/lib.rs

tests/exec.c

tests/expected/exec.stderr

tests/expected/exec.stdout