Set protobuf_MODULE_COMPATIBLE before any find_package call

[traversaro]

🦟 Bug fix

Fixes #956

Summary

In some environments where Protobuf is compiled using CMake (so not in debian-based distributions, as there protobuf is compiled via autotools), it is necessary to set the protobuf_MODULE_COMPATIBLE variable before any call to find_package, as any call to find_package could call transitively find_package(protobuf).

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
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[chapulina]

Thanks, @traversaro ! I'll see if I can retarget at ign-gazebo3 so we can get the fix from Citadel onwards.

[chapulina]

Rebased to Citadel, just waiting for CI.

I'll also cross-reference #501, which originally added protobuf_MODULE_COMPATIBLE to Edifice, and hasn't been backported because it includes other breaking changes.

[codecov]

Codecov Report

Merging #957 (9d2d7e9) into ign-gazebo3 (a83f56f) will not change coverage.
The diff coverage is n/a.

❗ Current head 9d2d7e9 differs from pull request most recent head 8650a5c. Consider uploading reports for the commit 8650a5c to get more accurate results

@@             Coverage Diff              @@
##           ign-gazebo3     #957   +/-   ##
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  Coverage        77.90%   77.90%           
============================================
  Files              221      221           
  Lines            12678    12678           
============================================
  Hits              9877     9877           
  Misses            2801     2801           

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