Build connectivity JNI against libc++_static

Instead of including the whole libc++ library by linking it dynamically,
use the static version so that unused symbols can be stripped.

This allows reducing the APEX size by 1MB (3.7MB -> 2.7MB), as otherwise
libc++ is included twice for 32 and 64 bit variants.

Bug: 171540887
Test: Device boots and has connectivity, size reduced

Change-Id: Ia66d795cf23d6f45997278300c103976433f7c5c