https://github.com/phaag/nfdump/pull/336

From e882722e4e006d0440fb5a37fb051d4747e4f225 Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Thu, 24 Mar 2022 22:50:13 +0000
Subject: [PATCH] Makefile.am: add ACLOCAL_AMFLAGS

Per autoconf docs [0], if using automake and AC_CONFIG_MACRO_DIR,
we need to include ACLOCAL_AMFLAGS in Makefile.am.

So, let's set ACLOCAL_AMFLAGS = -I m4.

This sorts out an automake warning.

Signed-off-by: Sam James <sam@gentoo.org>
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,3 +1,4 @@
+ACLOCAL_AMFLAGS = -I m4
 
 SUBDIRS = . bin man doc