Multibit build for x265-8/10/12-bit

To build a version that can handle 8 bit, or 10 bit, or 12 bit videos, a patch is provided in the thirdparty subdirectory that needs to be applied to do so. Be aware that the compile may take more time and seems to be about twice as long. To apply the required patch:

cd /path/to/cinelerra-5.1/thirdparty
patch < compile_multibit_X265.txt
mv x265_3.5.patch* src/.

Render formats h265-10bit and h265-12bit have been provided and will be operational after the applied patch is compiled in.