* configure.ac (AC_CHECK_FUNCS_ONCE, AC_SYS_LARGEFILE): Rely on
gnulib for strtok_r and large file support.
(AC_OBJEXT): Drop call now done by AC_PROG_CC.
(m4_foreach_w): Drop macro guaranteed by gnulib.
(AC_C_CONST): Drop call declared obsolete by autoconf.
Signed-off-by: NEric Blake <eblake@redhat.com>