alphasort doesn't have the right signature on bionic which causes the build to
fail. This implements a new bionic_alphasort function when building on bionic
providing the right signature and a functional equivalent of glibc's alphasort.

This signature problem with alphasort was fixed in upstream bionic but hasn't
been released yet. This commit can therefore be reverted as soon as the
following commit hits the Android NDK: 40e467ec668b59be25491bd44bf348a884d6a68d
Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>