[klibc] Fix m68k support

- fix syscall API and vfork
- support 6-argument syscalls
- add open/openat special handling for non-regparm arches

Signed-off-by: Thorsten Glaser <tg@mirbsd.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
9 files changed