build: apply autoconf suggestions

add -I m4 to Makefile for ACLOCAL_AMFLAGS
add macro dirs to configure_ac

Change-Id: Ied5ca518fedab65c63d0c89bcd0f21c3d32265e1
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index 08f5235..ddca382 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,3 +1,4 @@
+ACLOCAL_AMFLAGS = -I m4
 AM_DEFAULT_SOURCE_EXT = .cpp
 
 libblobcmdsdir = ${libdir}/ipmid-providers