aircrack-ng: needs toolchain with threads support

Fixes:
http://autobuild.buildroot.org/results/418c9385a9a5a5087a6790001560056d32cd9708



[Peter: drop iw comment]
Signed-off-by: Gilles Talis <gilles.talis@gmail.com>
Acked-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>