Make VLC 2.0.6 build again

Working around a couple of issues - vlc.git/contrib/src/ffmpeg/rules.mak points at ffmpeg HEAD which is unlikely to work ~months later, so I pointed it at ffmpeg n3.2.4. There is a dependency issue in contrib/src/iconv - it was assumed to be always installed on non-win32, which is not quite true in cross compilation - so add the proper check in there for that. This only manifests itself in builds with high parallelism - in a single threaded build, it works fine. Apparently libfreetype is (was?) missing from heanet SF mirror, so switched it.

libav v11.9 has text relocations on armeabi-v7a, so choose ffmpeg-n3.2.4