This will fix exporting meshes with armatures using Draco compression, like:
https://github.com/KhronosGroup/glTF-Blender-IO/issues/617
Differential Revision: https://developer.blender.org/D6342
Draco is added as a library under extern/ and builds a shared library that is
installed into the Python site-packages. This is then loaded by the glTF add-on
to do mesh compression.
Differential Revision: https://developer.blender.org/D4501