Add appropriate checks in configure.ac. Fixes a slew of autobuilder failures: http://autobuild.buildroot.org/results/cf6/cf6f5b6981694f74bfca45b3d04ff35e4226b162/ http://autobuild.buildroot.org/results/b34/b346472e686af5b517b689217349eab21878bb7b/ http://autobuild.buildroot.org/results/49a/49a6a2a88cac6e0899f271a5e65c78dd9eb2eab4/ ... Note: patches sent upstream, awaiting for reply... Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr> Cc: Gustavo Zacarias <gustavo@zacarias.com.ar> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>