Add annotations for exporting generated functions from a Windows DLL

[dawidcha]

I'm currently engaged in some work with gRPC aiming at merging a PR which permits gRPC to be built as a dynamic library under Windows (i.e. a DLL). here. gRPC makes use of μpb and needs to expose symbols generated by it from a DLL. That requires that the functions marked as extern be annotated with '__declspec(dllexport)' when compiled and '__declspec(dllimport)' when consumed.

For the protoc compiler, this is achieved by prefixing the file output location on the command line with dllexport_decl=MY_EXPORT_MACRO, and then defining MY_EXPORT_MACRO as either __declspec(dllimport) or __declspec(dllexport); or empty string, as appropriate, but this feature doesn't appear to be available in μpb.

Can something similar be added?

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[h-vetinari]

Not stale.

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[h-vetinari]

This is not stale, and there's an on open PR for this as well, at least in the context of upb (for now): #14981

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We triage inactive PRs and issues in order to make it easier to find active work. If this issue should remain active or becomes active again, please add a comment.

This issue is labeled inactive because the last activity was over 90 days ago.