Merge branch 'feature/support-manually-set-ninja-in-fortran-test' into 'master'

ref:core/dune-common Prior to this change the build program (make, Ninja) was
not identical to the one used by CMake, but the one installed on the system.

I found this when testing Fortran support of upcoming CMake 3.17 with upcoming
Ninja 1.10 - which works!

See merge request [!761]

  [!761]: gitlab.dune-project.org/core/dune-common/merge_requests/761