It is an ODR violation to use a template specialization for which an
explicit specialization is defined somewhere whose declaration is not
visible at the point of use.
Found via clang's -Wundefined-func-template warning.
Developers who want to enable it can either:
- *Temporarily* set ASSIMP_BUILD_BLENDER_DEBUG_DNA=1 in BlenderDNA.h, or
- *Temporarily* define ASSIMP_BUILD_BLENDER_DEBUG_DNA=1 on the build command line.
Addresses #3886.