Fix Qhull convex generation (second attempt)

[arntanguy]

Reverts #11

So, as it turns out, we need a combination of both the original method implemented by @ThomasDuvinage and the one I tried in #10. That is:

• For the same version of Qhull 2022.2 (8.0.2) it behaves differently on Ubuntu 22.04 and Nix:
  • On Ubuntu 22.04, we need to use the old c-style stream qhull.qh()->fout = out_stream;
  • On Nix, and probably more recent Ubuntu versions, we need to use the C++ stream interface std::stringstream output_stream; qhull.setOutputStream(&output_stream);

For now I could not find a reliable way to detect which should be used.

Useful context:

• Nice table summary of the multiple qhull libraries and their corresponding cmake targets: use same CMake target name for Debug and non-Debug qhull/qhull#76 (comment)

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[ThomasDuvinage]

Hello @arntanguy,
It also worth to mention that the current implementation is not compiling on windows for this specific line.

[arntanguy]

Hello @arntanguy, It also worth to mention that the current implementation is not compiling on windows for this specific line.

So we would need USE_LEGACY_QHULL_STREAM=OFF (modern c++ streams) on windows?