build: drop more redundant configure checks
build: drop more redundant configure checks

* 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: Eric Blake <a9da18479c871fe903d9590822cfe2629c6a4d11@redhat.com>

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