Add vfork() system call

-Same semantics as fork() as it's really just a stub
-Eases porting of BSD utilities

lib/nbsd_libc/stdlib/system.c

@@ -91,11 +91,7 @@ system(command)
 	}
 
 	(void)__readlockenv();
-#ifdef __minix
-	switch(pid = fork() ) {
-#else /* !__minix */
 	switch(pid = vfork()) {
-#endif /* !__minix */
 	case -1:			/* error */
 		(void)__unlockenv();
 		sigaction(SIGINT, &intsa, NULL);

lib/nbsd_libc/sys-minix/MISSING_SYSCALLS

@@ -76,4 +76,3 @@ futimes
 utrace
 uuidgen
 vadvise
-vfork

lib/nbsd_libc/sys-minix/Makefile.inc

@@ -16,7 +16,7 @@ SRCS+= 	accept.c access.c bind.c brk.c sbrk.c compat.S \
 	vectorio.c shutdown.c sigaction.c sigpending.c sigreturn.c sigsuspend.c\
 	sigprocmask.c socket.c socketpair.c stat.c statvfs.c symlink.c \
 	sync.c syscall.c sysuname.c truncate.c umask.c unlink.c write.c \
-	_exit.c _ucontext.c environ.c __getcwd.c
+	_exit.c _ucontext.c environ.c __getcwd.c vfork.c
 
 # Minix specific syscalls.
 SRCS+= cprofile.c lseek64.c sprofile.c _mcontext.c

lib/nbsd_libc/sys-minix/vfork.c

@@ -0,0 +1,16 @@
+#include <sys/cdefs.h>
+#include "namespace.h"
+#include <lib.h>
+
+#include <unistd.h>
+
+#ifdef __weak_alias
+__weak_alias(vfork, _vfork)
+#endif
+
+PUBLIC pid_t vfork()
+{
+  message m;
+
+  return(_syscall(PM_PROC_NR, FORK, &m));
+}

nbsd_include/unistd.h

@@ -289,6 +289,8 @@ int	 usleep(useconds_t);
 #ifndef __LIBC12_SOURCE__
 pid_t	 vfork(void) __RENAME(__vfork14);
 #endif
+#else
+pid_t	 vfork(void);
 #endif /* !__minix */
 
 #ifndef __AUDIT__