* If you use libgpr:
gpr is renamed to gnatprj
Like for gnatvsn, a compatibility gpr.gpr project is provided.
Context:
* Debian's gnat-6, like its predecessors, used to build a
Debian-specific libgnaprj.
* Around gnat-7 and AdaCore GPL/2017, the sources have moved from
gnat to gprbuild. The new name was libgnatprj.
Debian has renamed libgnatprj to libgpr in order to reduce divergence.
* Around 2018, it has appeared that another library had been using
the three-letter name since long before 2017. The name had to
change in Debian again.