libc: Sync asctime.c and localtime.c with tzcode2010a from elsie.
asctime.c: Set errno to EINVAL and return "??? ??? ?? ??:??:?? ????\n" if
asctime_r() is called with a NULL struct tm pointer.
(Note that asctime_r() is called by ctime_r() and asctime();
asctime() is called by ctime().)
localtime.c: Set errno to EINVAL and return WRONG if time1() is called with
a NULL struct tm pointer; avoid dereference if a NULL struct
tm pointer is passed to timelocal(), timegm(), or timeoff().
(Note that time1 is called by mktime(), timegm(), and timeoff();
mktime is called by timelocal().)