OS-3215 32bit syscalls with more than 6 parameters re-use arg0/arg1 as arg6/arg7
OS-3223 Passing arg6 and arg7 can't clobber the stack for ap-style calls
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Reviewed by: Keith M Wesolowski <wesolows@foobazco.org>