Make sure the m4 directory is created in autogen.sh

Later versions of autoreconf seem to expect ./m4 to exist, and I'd rather not
have an empy directory laying about, so for now, autogen.sh can just add it if
we don't have anything there yet

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>

autogen.sh

@@ -1,4 +1,5 @@
#! /bin/sh
set -x -e
mkdir -p m4
# --no-recursive is available only in recent autoconf versions
autoreconf -fv --install