Bug#957155: dune-grid: ftbfs with GCC-10

[Ansgar]

Control: found -1 2.7.0-1
Control: tag -1 + confirmed upstream
Control: owner -1 !

> The package fails to build in a test rebuild on at least amd64 with
> gcc-10/g++-10, but succeeds to build with gcc-9/g++-9.
[...]
> Name:      test-geogrid-yaspgrid
> FullName:  ./dune/grid/test/test-geogrid-yaspgrid
> Status:    FAILED
> Output:
[...]
>            Dune::GridError [checkIntersectionIterator:/<<PKGBUILDDIR>>/dune/grid/test/checkintersectionit.hh:518]: Could not find inside entity through intersection iterator on outside entity.

This is not fixed by 2.7.0.  Will look at it later.

Ansgar