Check that TCGETS is indeed the way to go

Please check if TCGETS is appropriate here: https://github.com/mattn/go-isatty/blob/13e91bf4058fb93d5629deb7b2e3763ec8f4fdf8/isatty_tcgets.go#L11 See https://git.musl-libc.org/cgit/musl/patch/?id=2de85a985654d2c944931267645d9a0686242dfe for details.