Take over the maintenance of some older macros from Autoconf. * m4/error.m4 (AC_FUNC_ERROR_AT_LINE): New macro, from GNU Autoconf. * m4/lstat.m4 (AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK): New macro, from GNU Autoconf. * m4/memcmp.m4 (AC_FUNC_MEMCMP): New macro, from GNU Autoconf. * m4/mktime.m4 (AC_FUNC_MKTIME): Change comment. Signed-off-by: Eric Blake <eblake@redhat.com>