semtimedop: add time64 syscall support, decouple 32-bit time_t

semtimedop: add time64 syscall support, decouple 32-bit time_t

time64 syscall is used only if it's the only one defined for the arch,
or if the requested timeout does not fit in 32 bits. on current 32-bit
archs where time_t is a 32-bit type, this makes it statically
unreachable.

on 64-bit archs, there is no change to the code after preprocessing.
on current 32-bit archs, the time is passed via an intermediate copy
to remove the assumption that time_t is a 32-bit type.

to avoid duplicating SYS_ipc/SYS_semtimedop choice logic, the code for
32-bit archs "falls through" after updating the timeout argument ts to
point to a [compound literal] array of longs. in preparation for
"time64-only" 32-bit archs, an extra case is added for neither SYS_ipc
nor the non-time64 SYS_semtimedop existing; the ENOSYS failure path
here should never be reachable, and is added just in case a compiler
can't see that it's not reachable, to avoid spurious static analysis
complaints.