build: add suggested m4 pieces from autotools

The configure step provided suggestions to add m4 explicit directory
pieces into the configure_ac and makefile_am.

Change-Id: Ic3862c384d5b42abaf798da65a5c6a89ee619c7b
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index 3d598ba..04e71f7 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,3 +1,4 @@
+ACLOCAL_AMFLAGS = -I m4
 AM_DEFAULT_SOURCE_EXT = .cpp
 
 libi2ccmdsdir = ${libdir}/ipmid-providers