Incorrect CS8911 for 'global using unsafe' with pointer type

[Sergio0694]

Version Used: 4.13.0-3.25105.4 (400efa2) (and tested both VS 17.13.0 and VS 17.14 P1)

Steps to Reproduce:

1. Checkout microsoft/CsWinRT@443d0c4
2. Open src\cswinrt.sln
3. Build WinRT.Runtime2.csproj

Ignore errors from other projects, just build this one project (it doesn't reference anything else).

Diagnostic Id: CS8911

Expected Behavior:

The code should compile just fine.

Actual Behavior:

The compiler produces an incorrect error:

cc. @CyrusNajmabadi

[Sergio0694]

It seems this is related to function pointers in particular:

// This fails to build
global using unsafe PFNCONTEXTCALL = delegate*<void>;

// This builds fine
global using unsafe PFNCONTEXTCALL = void*;