grass: 6.4.0RC6 -> 7.0.1

[vbgl]

This is a rewrite from scratch of the grass derivation.

This addresses #9160; @mucaho: would you like to test?

Briefly tested on linux-x86_64.

[mucaho]

Thanks again for your effort @vbgl !
Your nix expression compiles fine, however subversion and a gcc are missing as run-time dependencies on my system.
Unfortunately I wasn't able to call Grass geo-algorithms from QGis, but that's not a blocking issue.

[vbgl]

however `subversion` and a `gcc` are missing as run-time dependencies on my system.

Does it work if these dependencies are installed by other means (e.g., separate invocations of `nix-env -i`)?

Unfortunately I wasn't able to call `Grass` geo-algorithms from `QGis`, but that's not a blocking issue.

I don’t really know how to test that… I’ve updated this PR to enable GRASS support into QGIS: some more libraries are built. But it does not seem to be enough: nothing related to GRASS show up in the plug-in menu. Thanks.

[mucaho]

Does it work if these dependencies are installed by other means (e.g., separate invocations of nix-env -i)?

Yes, that fixes the issue. I also propose adding a runtime wrapper to grass, so that these runtime dependencies get installed and linked to the executable automatically (possibly like vbgl#1).

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But it does not seem to be enough: nothing related to GRASS shows up in the plug-in menu.

On my machine using your new qgis expression, the grass algorithms show up, but still complain about missing dependencies. You bring up the toolbox by clicking on the menu item Processing -> Tollbox and then you have to switch to advanced interface at the bottom of this toolbox. They should show up as Grass GIS 7 commands.

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I’ve updated this PR to enable GRASS support into QGIS

Hmm, could the grass build dependency be made optional and disabled by default? I don't think it should be mandatory to always install grass alongside qgis.

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As a side note, there is a special directory applications/gis for gis applications. Would it make sense to move the grass expression there?

[vcunat]

Looks good to me.