Reduce warnings

src/header/assert/mod.rs

src/header/netdb/linux.rs

src/header/netdb/mod.rs

src/header/regex/mod.rs

src/header/stdio/default.rs

src/header/stdio/helpers.rs

src/header/stdio/mod.rs

src/header/stdio/printf.rs

src/header/string/mod.rs

src/header/strings/mod.rs

src/header/sys_ioctl/mod.rs

src/header/sys_stat/mod.rs

src/header/sys_utsname/mod.rs

src/header/unistd/getopt.rs

src/header/unistd/mod.rs

src/lib.rs

src/platform/linux/mod.rs

src/platform/pal/mod.rs

src/platform/pal/signal.rs

src/start.rs