package/sdbusplus: create m4 directory before autoreconf

Commit d255b679 fixed the handling of
the a package local m4/ directory which might be missing. But this
only works if it is the very first argument. But for this package this
is not possible because we already occupy this with the extra include
directory for autoconf-archive. Bring back the hook to create the m4/
directory to fix this.

Fixes:

  http://autobuild.buildroot.net/results/dc907421a343b8523b14fc9a846e0caf7abe630c/



Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>