Remove GZ_SINGLETON_DECLARE definition workaround (fix for armhf)

[j-rivero]

Signed-off-by: Jose Luis Rivero jrivero@osrfoundation.org

🦟 Bug fix

Fixes #3208.

Summary

The trick of defining the template function specialized was introduced in a commit part of the Windows works as part of the Windows works, seems to me like a workaround to make the compilation to work somehow. On my Jammy testing system, both clang and gcc compiled it fine with this PR and packages were made using gcc for arm64, armhf and ppc64.

Did not test it on Windows, let's see if the CI is happy or it was indeed needed.

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)
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• All tests passed (See test coverage)
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[traversaro]

Did not test it on Windows, let's see if the CI is happy or it was indeed needed.

Sorry, I forgot about this PR. The conda-forge CI seems to be happy, the Windows 7 one tests are failing but I guess this is expected, so I guess we are good to go?

[talregev]

@j-rivero can you rebase this branch to the latest gazebo11?

[j-rivero]

@j-rivero can you rebase this branch to the latest gazebo11?

I can rebase and merge yes.