package/libbsd: depends on architectures providing a.out.h

libbsd requires a.out.h, which is only available in a select subset
of the architectures Buildroot supports.

Propagate these new dependencies down to libedit.

Fixes:
    http://autobuild.buildroot.org/results/019/019091312ec547520370ffad967b53e23f54a14b
    http://autobuild.buildroot.org/results/87c/87c3a8bf2248606d80ddcfd96132de4c5fe869ed
    http://autobuild.buildroot.org/results/589/5891f539ce3f3ff2e3411228472c8833fdd0d7c0


    [...]

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>