libbsd: needs wide character support

libbsd: needs wide character support

Commit d879be30495 (package/libbsd: enable for non-glibc toolchains)
enabled build of libbsd with uClibc. libbsd requires wchar support.
Disable libbsd when uClibc does not provide wchar support.

Fixes:
http://autobuild.buildroot.net/results/4fb/4fb576c644a7322730658ed585bcc4a353a42e85/
http://autobuild.buildroot.net/results/459/45946f11524c57ffa59bf88d4a2ea0d4933fa851/
http://autobuild.buildroot.net/results/ee3/ee3ad5172d6a218dfde4cf3e9fecf1906b0fc642/

Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>