Fix cross-compilation support for gz-msg10

[traversaro]

🦟 Bug fix

Fixes #390

Summary

This PR adds a way to cross-compile gz-msgs10. This is done by defining three CMake options to overload all the executable involved in the message generation process. The workflow is documented with a comment in the CMakeLists.txt (the basic idea is that if you need to cross-compile, probably you know that you know how to read basic code). The main difference w.r.t. to the past is that now code generation happens also in some downstream projects, so this variables need to be set also in downstream projects to cross-compile the downstream projects.

I am not super happy about this solution as it adds a lot of CMake argument parsing boilerplate, but it seem to be working fine and I do not have any concrete idea on how to improve , so I thought it made sense to submit it in this form.

Related past PRs:

• Add CMake options to support cross-compilation #60
• Fix cross-compilation workflow #319

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #392 (e22b64a) into gz-msgs10 (0f69062) will not change coverage.
The diff coverage is n/a.

❗ Current head e22b64a differs from pull request most recent head bf628d2. Consider uploading reports for the commit bf628d2 to get more accurate results

@@            Coverage Diff             @@
##           gz-msgs10     #392   +/-   ##
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  Coverage      97.26%   97.26%           
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  Files             27       27           
  Lines           1170     1170           
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  Hits            1138     1138           
  Misses            32       32