bsd-user: Start translation of arch-specific sysctls

bsd-user: Start translation of arch-specific sysctls

Intercept some syscalls that we need to translate (like the archiecture
we're running on) and translate them. These are only the simplest ones
so far.

Signed-off-by: Juergen Lock <nox@jelal.kn-bremen.de>
Co-Authored-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Stacey Son <sson@FreeBSD.org>
Co-Authored-by: Warner Losh <imp@bsdimp.com>
Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>