buildsystem: add an option to build C++ code with static runtime

By default we use the dynamic runtime and need to ship libc++_shared.so.

This needs the counterpart on the libvlcjni script so that all our code is built with the same C++ runtime configuration.

Will need libvlcjni!148 (merged) and libvlcjni!152 (merged) to work on all targets.

Required for libvlcjni!152 (merged)