Adding Boost via cpm

[dcoeurjo]

PR Description

Adding boost via CPM (not working yet because of BoostAddons --ping @BDoignies--).

Checklist

• Unit-test of your feature with Catch.
• Doxygen documentation of the code completed (classes, methods, types, members...)
• Documentation module page added or updated.
• New entry in the ChangeLog.md added.
• No warning raised in Debug mode.
• All continuous integration tests pass (Github Actions)

[dcoeurjo]

Issue at cmake when adding boost::headers to the BoostAddons target... I'm not sure to understand the EXPORT issue. Any idea, @BDoignies ?

[BDoignies]

Yes, you need to add the library "boost_headers" (not BOOST::Headers because this is an aliased name) to the things that are exported with the libraries.

I think this is because there is no export rules in the boost.cmake file (unlike eigen.cmake:81)

I am not sure where the boost.cmake comes from and left it untouch. But this is probably more appropriate to modify this file instead. Especially since the "boost_headers" target is somewhat obscure and not used directly in the linking process...

[BDoignies]

Note: before sending the commit, I have not tried to compile the code, just to run the cmake. Looking at the error message, some boost/libraries are missing when creating the targets.

[dcoeurjo]

Ok thx, the boost.cmake comes from adobe/lagange.

[BDoignies]

My commit should clean up cmake and work (hopefully).

When tried locally, DGtalTools was still linking to system boost. Fixing this requires a PR in DGtalTools to link against the correct boost library. As long as there are no boost cpp files in use, this should not be a problem.