Add support for dynamic libraries under Visual Studio

[lemire]

Currently, we can build CRoaring as either a shared or static library (by default as a shared library, but static with BUILD_STATIC=ON).

This works on posix systems (macOS and Linux) but for Visual Studio, we need to default on BUILD_STATIC=ON.

For Visual Studio to support dynamic libraries, we probably need extra code (e.g., __declspec(dllexport) calls?)

[lemire]

c.c. @ksajme

[madscientist]

Honestly, I'm not sure what the use-case is for a CRoaring DLL... would someone really want a sparse bitmap library as a DLL?

As you mention it is some extra work dealing with export etc. If it were me I'd wait until someone actually wants it, before spending time on it. But of course, YMMV! :)

[lemire]

@madscientist I think it is useful to document that we do not support building a dynamic library under Visual Studio currently.

[madscientist]

@lemire Agreed. It's always better if these things aren't a surprise...

[KingJiangNet]

I have wrapped it into a VS project: https://github.com/KingJiangNet/CRoaring.Net/tree/master/src/CRoaring

[lemire]

@KingJiangNet Right. So it would not be very difficult for us to integrate this into the main code.

[lemire]

Fixed in release 0.2.22.