add missing ACLOCAL_AMFLAGS

This package puts m4 files in config/ but doesn't set the right -I flags
which leads to random errors with autoreconf.  Declare it properly.

BUG=chromium-os:39738
TEST=`emerge-x86-alex dbus-c++` still works

Change-Id: I0235cb96eb184a4c5b18c24ef6e32382e5493d81
Reviewed-on: https://gerrit.chromium.org/gerrit/45037
Reviewed-by: Chris Masone <cmasone@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/Makefile.am b/Makefile.am
index 29bb7c9..1bb7268 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -2,6 +2,8 @@
 
 EXTRA_DIST = autogen.sh libdbus-c++.spec libdbus-c++.spec.in
 
+ACLOCAL_AMFLAGS = -I config
+
 pkgconfigdir = $(libdir)/pkgconfig
 pkgconfig_DATA = dbus-c++-1.pc