Thread safe Coin.

[veelo]

@Rexbas I was wondering: Does FreeCAD use precompiled Coin, or are you configuring with non-default options? We rely on -DCOIN_THREADSAFE=ON (and we use -DUSE_SUPERGLU=ON) so we compile ourselves. Which is not a big deal, but I am wondering if the defaults match the typical use. According to the docs there is an overhead to -DCOIN_THREADSAFE=ON, so I understand why it is currently OFF.

I am not suggesting that we should add this to the build matrix, as it is already rather large, but it would be interesting to know what everybody uses.

[Rexbas]

FreeCAD uses the coin3d conda package. This is what I can find about how that is build: https://github.com/conda-forge/coin3d-feedstock/blob/main/recipe/build.sh. The coin in the FreeCAD flatpak is build like this: https://github.com/flathub/org.freecad.FreeCAD/blob/master/org.freecad.FreeCAD.yaml#L177-L212. There were also disscussions about vendoring coin and pivy into FreeCAD: FreeCAD/FreeCAD#18883. But that is still a work in progress I guess. So it seems we use defaults for DCOIN_THREADSAFE.

[veelo]

Thanks.