CMake silently downloads Thrust

[mmuman]

I tried building OpenSCAD in the train yesterday, I had all the submodules and packaged dependencies installed… and wasted an hour retrying because the connection was barely working, and I didn't even know how far it went, because it just seemed to hang on "Parallel Backend: TBB", and I had to look up the processes to find out. Then I tried disabling it but couldn't find how…

At the very least it should tell what it is doing.

[elalish]

Sure, that sounds reasonable. Would you like to tweak our CMake?

[mmuman]

Been busy with FOSDEM and other stuff, might have a try later.

[mmuman]

Oh great, one less thing on my TODO list, thanks!