Allow C# projects to contain multiple file types

[tschoonj]

This allows for linking a C# executable against a C++ .NET assembly that was generated in the same project.

[tschoonj]

This fix is probably too simple, even though it actually fixes my problem...

Any thoughts how this could be improved upon? Basically, linking a C# executable against a DLL should not add a C++ compiler to self.compilers.

[dcbaker]

At the very least we need a test for this, but I'm not even sure how you output .net assembly from c++ and whether what we really need is a donet() target like the jar() target, or what.

[tschoonj]

With the patch in this PR I managed to compile the C++ .NET assembly and use it successfully from C#:

https://github.com/tschoonj/xraylib/blob/8c082b576da211ff915222c64e3de2b47c7872d2/csharp/meson.build

[tschoonj]

I should be able to come up with a test for this, I will do that when I have some time later.

[tschoonj]

It looks to me as if the C++ compiler generates a 32-bit dll, but csc produces a 64-bit executable.

Is there anything I can do to ensure that both produce output for the same architecture?

Thanks!

[tschoonj]

@dcbaker any thoughts on how to fix the build?

Thanks!

[dcbaker]

I'll have to think about it some more, i've been putting off getting out my windows machine for a while now, I may have to go ahead and do that.

[tschoonj]

Something that surprises me is that vc2017x86ninja appears to be the only build where the C# tests are run, as they are skipped on the other vc build.