Use C string literals & deprecate `c_str!`

src/c_str.rs

src/header/dlfcn/mod.rs

src/header/getopt/mod.rs

src/header/grp/mod.rs

src/header/netdb/host.rs

src/header/netdb/linux.rs

src/header/netdb/mod.rs

src/header/netdb/redox.rs

src/header/pty/linux.rs

src/header/pty/redox.rs

src/header/pwd/mod.rs

src/header/stdio/mod.rs

src/header/unistd/getpass.rs

src/header/unistd/mod.rs

src/ld_so/linker.rs

src/macros.rs

src/platform/redox/epoll.rs

src/platform/redox/mod.rs

src/platform/test/mod.rs