blosc embedded a copy of zlib/pthreads causing duplicate symbol linker errors. pthreads was windows specific, but zlib may apply to other platforms as well.
Note these are intended for platform maintainers, we do not intend to
support users making their own builds with these. For that precompiled
libraries from lib/ should be used.
Implemented by Martijn Berger, Ray Molenkamp and Brecht Van Lommel.
Differential Revision: https://developer.blender.org/D2753
