Since no system call takes more than 6 arguments, and no more than one

Since no system call takes more than 6 arguments, and no more than one
off_t argument, there is no need to process more than 6 arguments on
64-bit platforms and 8 on 32-bit platforms.

Make the syscall argument gathering code simpler by removing never-used code
to fetch more arguments from the stack, and local argument arrays when pointing
to the trap frame does the job.

ok guenther@ jsing@