toolchain/microblaze: fix up big-endian characteristics

The big-endian microblaze external toolchain is missing vital
characteristics being set, such as LARGEFILE support, IPV6 and so on.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Tested-by: Stephan Hoffmann <sho@reLinux.de>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>