Regression tests for system calls ported from NetBSD.

Reimplement ATF with many hacks to adjust the tests as little as possible.

Tests passing without source file adjustments:
t_access	t_getsockname	t_msgctl	t_sigaltstack
t_bind		t_gettimeofday	t_msgsnd	t_socketpair
t_conect	t_kill		t_msync		t_truncate
t_getgroups	t_link		t_pipe		t_umask
t_getitimer	t_listen	t_ppoll		t_write
t_getlogin	t_minherit	t_sendrecv
t_getpid	t_mkdir		t_setuid
t_getsid	t_mkfifo	t_sigaction

Tests passing after adjustments:
t_chroot		- fchroot is not implemented
t_clock_gettime		- requires sysctlbyname
t_dup			- OpenBSD dup3 is similar to Linux dup3
t_fork			- add reallocarr function, remove clone(2) tests
t_fsync			- replace mkstemp
t_getrusage		- no expected fail, PR kern/30115 is NetBSD, work more
t_kevent		- no EVFILT_USER, DRVCTLDEV, passing kqueue forbidden
t_mknod 		- remove tests for unsupported file types
t_msgget		- remove msgget_limit test
t_poll 			- remove pollts_* tests
t_ptrace 		- change EPERM -> EINVAL for PT_ATTACH of a parent
t_revoke 		- remove basic tests, revoke only on ttys supported
t_select 		- remove sigset_t struct as it is int on OpenBSD
t_setrlimit		- remove unsupported resource parameters and lwp
t_syscall		- add __syscall prototype
t_vfork			- SIGSTOP is masked before exec(3)/exit(3)
t_wait_noproc		- waitid and wait6 are not implemented
t_wait_noproc_wnohang	- waitid and wait6 are not implemented

Failing tests:
t_mlock		- wrong errno, succeeds where not expected, POSIX imprecise
t_mmap		- ENOTBLK on test NetBSD is skipping, remove mmap_va0 test
t_msgrcv	- msgrcv(id, &r, 3 - 1, 0x41, 004000) != -1
t_pipe2 	- closefrom(4) == -1, remove F_GETNOSIGPIPE and nosigpipe test
t_stat 		- invalid GID with doas
t_unlink	- wrong errno according to POSIX

Excluded tests:
t_clock_nanosleep	- not available
t_clone			- not available
t_futex_ops		- no lwp
t_futex_robust		- no lwp
t_getcontext		- not available, removed in POSIX.1-2008
t_getrandom		- not available
t_issetugid		- works as iplemented
t_lwp_create		- not available
t_lwp_ctl		- not available
t_mincore		- removed
t_mprotect		- no exec_prot_support and no return_one in libc
t_nanosleep		- not available
t_pollts		- not available
t_posix_fadvise		- optional POSIX Advisory Information
t_posix_fallocate	- optional POSIX Advisory Information
t_ptrace_sigchld	-
t_ptrace_wait		-
t_ptrace_wait3		-
t_ptrace_wait4		-
t_ptrace_wait6		- not implemented
t_ptrace_waitid		-
t_ptrace_waitpid	-
t_sigqueue		- not implemented, added in POSIX.1-2004
t_sigtimedwait		- not implemented, added in POSIX.1-2004
t_swapcontext		- not available, removed in POSIX.1-2008
t_timer_create		- not implemented, added in POSIX.1-2004
t_ucontext		- not available, removed in POSIX.1-2008
t_wait			- wait6 is not available, not POSIX