This means that librtmp is no longer required as ffmpegs internal rtmp
code is now used instead. libgmp is now a direct dependency as it is
used for rtmp crypt functions.

This changes the output directory. All dependencies will need to be
updated to latest git and rebuilt to ensure they are in the correct
location.

OpenCl was causing issues with users without proper opencl support
failing to load built dll's. Since it only adds 2 rarely used filters
its not worth keeping.