Use m4 directory

Use m4 directory

- Follow the suggestion by libtoolize:
   "Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.ac and
    rerunning libtoolize, to keep the correct libtool macros in-tree.
    Consider adding `-I m4' to ACLOCAL_AMFLAGS in Makefile.am."
  and add the macro and define.

- Create the m4 directory and move acinclude.m4 as xcb.m4 there.

- Ignore the m4 files libtoolize copies into the m4 directory
  (m4/l*.m4).

Signed-off-by: Daniel Martin <consume.noise@gmail.com>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Uli Schlachter <psychon@znc.in>
Tested-By: Ran Benita <ran234@gmail.com>