Fix dllimport code generation for module symbols

[kaadam]

[bryanpkc]

Please add a test case?

[bryanpkc]

If Flang always generates dllimport attribute for global symbols, do we still need the PGDLL macro and !DEC$ ATTRIBUTES DLLEXPORT in the runtime?

[kaadam]

Please add a test case?

@bryanpkc This test would be Windows specific. Currently we're not able to run Flang tests on Windows, what about the policy in this case?

[bryanpkc]

@kaadam Sorry I didn't see your question! I think GitHub actually provides Windows runners:

https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners#supported-runners-and-hardware-resources

Do you think we could leverage them to set up some CI jobs on Windows?

[kiranchandramohan]

This needs a rebase.