Respect SupportedOSPlatformAttribute on exports.

[AaronRobinsonMSFT]

Add tests for all currently defined .NET platforms.

Fixes #82

[AaronRobinsonMSFT]

@jkoritzinsky Could you do me a favor and give this a quick pass? I don't see any need for UnsupportedOSPlatformAttribute for native exporting but could be missing something.

[jkoritzinsky]

This generally looks good. I think implementing the whole spec for these attribute types would be useful, primarily for cases that might use some sort of underlying APIs that only work on some platforms (or to enable the UnmanagedCallersOnly method to use methods with UnsupportedOSPlatformAttribute in managed code and have that reflected properly in the native exports without causing analyzer diagnostics).

I'd suggest doing #ifndef for the "unsupported OS" cases, which should be pretty simple.

[AaronRobinsonMSFT]

I'd suggest doing #ifndef for the "unsupported OS" cases, which should be pretty simple.

Sigh... fine :-) It is simple for sure.

[AaronRobinsonMSFT]

I think implementing the whole spec for these attribute types would be useful

Ugh. This is more complicated since multiple are allowed.... boo.