kselftests: depend on clang-native for BPF target
kselftests: depend on clang-native for BPF target

Some .o files needed by the bpf selftests were not being
produced because version 3.7+ of Clang was needed, with
support for the BPF target.

This has been done on the other kselftests packages for some
time now.

Signed-off-by: Daniel Díaz <81c1e6f46dfb75ebff90afb11720614d43e597b3@linaro.org>

kraj/meta-96boards,mrchapp/meta-96boards,kraj/meta-96boards,96boards/meta-96boards