[6.0] 5ce486945 build: Enable automake's subdir-objects option

[Dridi Boukelmoune]

commit 5ce48694594709bb1faa967f3922a4841777cbc3
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Wed Jul 1 14:00:03 2020 +0200

    build: Enable automake's subdir-objects option
    
    We can get rid of autogen.des' egrep command used to silence this
    warning too. In fact we can even remove the subshell and simply
    call autoreconf directly. The problem with egrep is the loss of
    a meaningful exit status for the autoreconf invocation.
    
    I also enabled autoreconf's verbose output.
    
    Conflicts:
            autogen.des

diff --git a/autogen.des b/autogen.des
index 0cc52dc42..c066ee8d3 100755
--- a/autogen.des
+++ b/autogen.des
@@ -22,8 +22,8 @@ else
 	DST="--prefix=/opt/varnish --mandir=/opt/varnish/man"
 fi
 
-rm -f configure
-(cd $SRCDIR && . ./autogen.sh 2>&1 | egrep -v "(subdir-objects|is in a subdirectory)")
+rm -f $SRCDIR/configure
+(cd $SRCDIR && . ./autogen.sh 2>&1)
 
 # autoconf prior to 2.62 has issues with zsh 4.2 and newer
 export CONFIG_SHELL=/bin/sh
diff --git a/configure.ac b/configure.ac
index 1fc8d677c..f3024becd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -19,7 +19,7 @@ AC_CANONICAL_SYSTEM
 AC_LANG(C)
 
 AM_MAINTAINER_MODE([disable])
-AM_INIT_AUTOMAKE([1.11 foreign color-tests parallel-tests])
+AM_INIT_AUTOMAKE([1.11 foreign color-tests parallel-tests subdir-objects])
 AM_SILENT_RULES([yes])
 AC_DISABLE_STATIC
 AC_PROG_LIBTOOL