Move AC_CONFIG_AUX_DIR up a few lines so the autotools can find it

This patch is based on the same solution adopted by Debian:

  https://lists.debian.org/debian-release/2014/11/msg01231.html

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>

diff -rup a/configure.ac b/configure.ac
--- a/configure.ac	2014-02-09 11:52:42.000000000 +0000
+++ b/configure.ac	2015-01-06 15:07:10.003074775 +0000
@@ -13,11 +13,12 @@ m4_include([version.m4])
 AC_PREREQ([2.61])
 AC_INIT([libmemcached],VERSION_NUMBER,[http://libmemcached.org/])
 
+AC_CONFIG_AUX_DIR([build-aux])
+
 # Setup the compilers early on
 AC_PROG_CC([cc gcc clang])
 AC_PROG_CXX([c++ g++ clang++])
 
-AC_CONFIG_AUX_DIR([build-aux])
 AC_CONFIG_MACRO_DIR([m4])
 
 AC_CANONICAL_HOST