Re: kern/56673: don't allow execve with NULL argv

[Jan Schaumann <jschauma%netmeister.org@localhost>]

If we already reject argv == NULL itself, as noted by
mrg@, then I really don't see a good argument to allow

    char *argv[1] = { 0 };

POSIX does not appear to prohibit enforcing argv[0] to
be non-NULL, and while it may at the same time _allow_
argv[0] == NULL, it strikes me as entirely reasonable
to prevent what almost inevitably is problematic.

While we can fix all code in the NetBSD source tree to
not assume argv[0] != NULL, we cannot do the same for
all add-on software.  Preventing errant use of
(albeit permissible) coding errors makes for a more
robust OS.