unix: fix OpenBSD codegen to include F_OK

F_OK is used with access(2), but it was removed for openbsd/amd64 when
generated code was updated to OpenBSD 6.3 in 7f59abf3.

Fixes golang/go#26593

Change-Id: I4a542506b1045f0c860bb3137c4d81149a5e1cae
Reviewed-on: https://go-review.googlesource.com/126635
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/mkerrors.sh

@@ -261,6 +261,7 @@ includes_OpenBSD='
 #include <sys/sysctl.h>
 #include <sys/termios.h>
 #include <sys/ttycom.h>
+#include <sys/unistd.h>
 #include <sys/wait.h>
 #include <net/bpf.h>
 #include <net/if.h>

unix/zerrors_openbsd_amd64.go

@@ -472,6 +472,7 @@ const (
 	F_GETLK                           = 0x7
 	F_GETOWN                          = 0x5
 	F_ISATTY                          = 0xb
+	F_OK                              = 0x0
 	F_RDLCK                           = 0x1
 	F_SETFD                           = 0x2
 	F_SETFL                           = 0x4

unix/zsysnum_openbsd_amd64.go

@@ -116,6 +116,7 @@ const (
 	SYS_PSELECT        = 110 // { int sys_pselect(int nd, fd_set *in, fd_set *ou, \
 	SYS_SIGSUSPEND     = 111 // { int sys_sigsuspend(int mask); }
 	SYS_SENDSYSLOG     = 112 // { int sys_sendsyslog(const char *buf, size_t nbyte, \
+	SYS_UNVEIL         = 114 // { int sys_unveil(const char *path, \
 	SYS_GETSOCKOPT     = 118 // { int sys_getsockopt(int s, int level, int name, \
 	SYS_THRKILL        = 119 // { int sys_thrkill(pid_t tid, int signum, void *tcb); }
 	SYS_READV          = 120 // { ssize_t sys_readv(int fd, \