[CYGWIN][MINGW] Remove DJINTEROP_PUBLIC, enum doesn't export symbols

[carlo-bramini]

I tried to build libdjinterop with both MinGW and Cygwin, but this error comes out:

include/djinterop/engine/engine_schema.hpp:31:29: error: ‘dllexport’ attribute ignored [-Werror=attributes]
   31 | enum class DJINTEROP_PUBLIC engine_schema
      |                             ^~~~~~~~~~~~~

In my opinion, this error is correct because an enum does not generate binary symbols, so GCC tells us that the attribute has no effect and the -Werror option handles it as an error.
I could not understand why it has been done here too because PR #142 doesn't write any information about the reasons of this change.
In my opinion, this attribute must be removed from that point.
Perhaps MSVC tolerates it, but a more strict compiler like GCC does not.

[mr-smidge]

Hi @carlo-bramini , thanks for this - I agree with your suggestion that putting dllexport on the enum is incorrect, so the PR looks good.

How do you feel about also adding a new entry in .github/workflows/cmake.yml on Windows 2025 making use of msys2 to prove that this works? https://github.com/actions/runner-images/blob/main/images/windows/Windows2025-Readme.md#msys2

Please may you also bump up the patch version number in CMakeLists.txt? (to 0.27.3)

Thank you!

[carlo-bramini]

How do you feel about also adding a new entry in .github/workflows/cmake.yml on Windows 2025 making use of msys2 to prove that this works? https://github.com/actions/runner-images/blob/main/images/windows/Windows2025-Readme.md#msys2

I think that's a good idea, but unfortunately I never played with workflows at the moment, so I don't know how this works and it could be done, I'm sorry.

Please may you also bump up the patch version number in CMakeLists.txt? (to 0.27.3)

I added an extra commit with this change.
Thank you very much for your quick reply.

[mr-smidge]

How do you feel about also adding a new entry in .github/workflows/cmake.yml on Windows 2025 making use of msys2 to prove that this works? https://github.com/actions/runner-images/blob/main/images/windows/Windows2025-Readme.md#msys2

I think that's a good idea, but unfortunately I never played with workflows at the moment, so I don't know how this works and it could be done, I'm sorry.

No worries, I can look into this another time.

LGTM otherwise, so happy to approve!