Mirror the linux-user practice and add a si_type argument to queue
signal. This will be transported as the upper 8 bits in the si_type
element of siginfo so that we know what bits of the structure are valid
and so we can properly implement host_to_target_siginfo_noswap and
tswap_siginfo. Adapt the one caller of queue_signal to the new
interface.  Use all the same names as Linux (except _RT which we don't
treat differently, unlike Linux), though some are unused. Place this
into signal-common.h since that's a better place given bsd-user's
structure. Move prototype of queue_signal to signal-common.h to mirror
linux-user's location.

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>