Blender Git Loki

Deduplicate CUDA and OpenCL wranglers

For now it was mainly about OpenCL wrangler being duplicated
between Cycles and Compositor, but with OpenSubdiv work those
wranglers were gonna to be duplicated just once again.

This commit makes it so Cycles and Compositor uses wranglers
from this repositories:

- https://github.com/CudaWrangler/cuew
- https://github.com/OpenCLWrangler/clew

This repositories are based on the wranglers we used before
and they'll be likely continued maintaining by us plus some
more players in the market.

Pretty much straightforward change with some tricks in the
CMake/SCons to make this libs being passed to the linker
after all other libraries in order to make OpenSubdiv linked
against those wranglers in the future.

For those who're worrying about Cycles being less standalone,
it's not truth, it's rather more flexible now and in the future
different wranglers might be used in Cycles. For now it'll
just mean those libs would need to be put into Cycles repository
together with some other libs from Blender such as mikkspace.

This is mainly platform maintenance commit, should not be any
changes to the user space.

Reviewers: juicyfruit, dingto, campbellbarton

Reviewed By: juicyfruit, dingto, campbellbarton

Differential Revision: https://developer.blender.org/D707