automake 1.14 and subdir-objects

[Nils Goroll]

The automake authors are planning to activate subdir-objects unconditionally:

http://lists.gnu.org/archive/html/automake/2013-06/msg00040.html

  - The next major Automake version (2.0) will unconditionally activate
    the 'subdir-objects' option.  In order to smooth out the transition,
    we now give a warning (in the category 'unsupported') whenever a
    source file is present in a subdirectory but the 'subdir-object' is
    not enabled.

automake 1.14 complains when building Varnish:

bin/varnishadm/Makefile.am:9: warning: source file
'$(top_srcdir)/lib/libvarnish/vsa.c' is in a subdirectory,
bin/varnishadm/Makefile.am:9: but option 'subdir-objects' is disabled
bin/varnishadm/Makefile.am:9: warning: source file
'$(top_srcdir)/lib/libvarnish/vtcp.c' is in a subdirectory,
bin/varnishadm/Makefile.am:9: but option 'subdir-objects' is disabled
(yaddayadda)

I have checked if we could enable subdir-objects now, but we basically run into
the dilemma summarized here: http://curl.haxx.se/mail/lib-2013-07/0172.html

IIUC, the punchline is that we may choose from these options:

- hope for automake maintainers fix subdir-objects and ignore the warnings for
  the time being
- use subdir-objects, but disable dependency tracking
- hack our Makefiles to work around (don't)

Nils