Unable to consume C# 7.2 stack-only types in VB 15.5

If I use stack only type in my VB code, error BC30668 will block compilation. I'm using VS2017 15.6.7.

### Steps to reproduce:
1. Create a .NET Core VB Console project.
2. Edit the .vbproj file, add `Latest` in ``.
3. Create a .NET Standard 2.0 C# class library.
4. Create a new C# code file, and add `public ref struct StackOnlyType {}` in that .cs file.
5. Upgrade the C# project to 7.2 .
6. In the VB console app, add reference to that C# project.
7. Add `Dim errorType As StackOnlyType` to `Sub Main`.
8. Build the whole solution.

### Expected behavior:
The code should compile, because I'm not trying to put a stack-only variable on the heap.

### Actual behavior:
Error: BC30668 "Types with embedded references are not supported in this version of your compiler"