Update autoconf prologue to use "foreign" strictness.

Upstream-Status: Pending
Signed-off-by: Ross Burton <ross.burton@intel.com>

diff --git a/configure.ac b/configure.ac
index d974461..a20dfa8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,7 +1,7 @@
 dnl Process this file with autoconf to produce a configure script.
 AC_INIT([which], [2.21])
 AC_CONFIG_SRCDIR(which.c)
-AM_INIT_AUTOMAKE
+AM_INIT_AUTOMAKE([foreign])
 AM_CONFIG_HEADER(config.h)
 AM_MAINTAINER_MODE