start-stop-daemon: fix build on non listed architectures

start-stop-daemon: fix build on non listed architectures

Not all Buildroot supported architectures are known to dpkg. Convert the
configure error to a warning.

Fixes:
http://autobuild.buildroot.net/results/24e/24e37550749dc15ed7223fd515fa4628803f341e/
http://autobuild.buildroot.net/results/445/445bf4742d78a0bf93b4c75dc733c4315530031e/
http://autobuild.buildroot.net/results/952/952051485f23b67ffc449360886d6757c385331f/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Tested-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>