cobalt/posix/io: Unify native and compat versions of select
Rather than duplicating lots of code for the sake of compat userspace accesses, provide a common version that is given a flag to decide whether to take the compat or regular code paths. This also brings restart support to the compat selection version which was forgotten by 36132cdb . Signed-off-by:Jan Kiszka <jan.kiszka@siemens.com>