Merge branch 'lockf_impl' into 'master'

src/c/fcntl.c

src/header/fcntl/mod.rs

src/header/stdio/helpers.rs

src/header/stdio/mod.rs

src/header/sys_ioctl/redox.rs

src/header/unistd/mod.rs

src/platform/linux/mod.rs

src/platform/pal/mod.rs

src/platform/redox/mod.rs