Fix warnings and add c_str

Makefile

src/c_str.rs

src/header/arpa_inet/mod.rs

src/header/ctype/mod.rs

src/header/dirent/mod.rs

src/header/fcntl/mod.rs

src/header/fenv/mod.rs

src/header/float/mod.rs

src/header/fnmatch/mod.rs

src/header/grp/mod.rs

src/header/inttypes/mod.rs

src/header/locale/mod.rs

src/header/netinet_in/mod.rs

src/header/semaphore/mod.rs

src/header/stdio/mod.rs

src/header/stdlib/mod.rs

src/header/string/mod.rs

src/header/strings/mod.rs

src/header/sys_ioctl/mod.rs

src/header/sys_mman/mod.rs