IDs of libavcodec, libavutil, libswresample, libswscale and libopenh264
are rewrote after they are installed in the OUTPUT directory instead of
at package generation time. Thus, the correct IDs are used while compiling
libraries which depend of these.

configs: define CMAKE_OSX_DEPLOYMENT_TARGET as minimum between current SDK used and current OSX version, so that if one is using 10.11 with an 10.10 SDK it still work