configure.ac: use AC_PROG_SED

It looks like AC_PROG_SED was added in 2.59b, and wasn't in the
original 2.59 in the original 2.59.  Presumably that's why, though
it could've been an oversight.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Matt Turner <mattst88@gmail.com>
1 file changed