PROJ.6 introduces a brand new API completely different from the traditional one adopted by PROJ.4
previous versions of libspatialite developed before the release of PROJ.6 can never be expected to support this new API.

suggested remedies:
- the latest libspatialite version (5.0.0-RC1) from the Fossil repository fully support the new PROJ.6 API
- PROJ.6 still continues to support the now deprecated old API, so it can be effectively linked to legacy spatialite versions.
  but enabling this option requires to define a special build time option:
  -DACCEPT_USE_OF_DEPRECATED_PROJ_API_H=1