Makefile.am: add ACLOCAL_AMFLAGS

Add ACLOCAL_AMFLAGS, a standard way to tell aclocal where to find
necessary macros.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

Author: lumag

Makefile.am

@@ -19,6 +19,7 @@
 # OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 # USE OR OTHER DEALINGS IN THE SOFTWARE.
 
+ACLOCAL_AMFLAGS = -I m4/m4
 AUTOMAKE_OPTIONS = dist-bzip2 dist-zip
 SUBDIRS = src doc
 EXTRA_DIST = README.* Release_Notes inet_ntop.c autogen.sh m4