fix building error for error: fallthrough annotation in unreachable code

[shushanhf]

/home/qiao/work_qiao/runtime/src/coreclr/interop/comwrappers.cpp:740:21: error: fallthrough annotation in unreachable code [-Werror,-Wimplicit-fallthrough]
                    FALLTHROUGH;
                    ^
/home/qiao/work_qiao/runtime/src/native/minipal/utils.h:25:25: note: expanded from macro 'FALLTHROUGH'
#    define FALLTHROUGH [[fallthrough]]

[shushanhf]

Hi, @jkotas
Who can help reviewing this PR?
Thanks

I find @AaronRobinsonMSFT @jkoritzinsky by https://github.com/dotnet/runtime/blob/main/docs/area-owners.md

[AaronRobinsonMSFT]

Is this on a Release or Debug/Checked build?

[AaronRobinsonMSFT]

The problem here, and something the above code now doesn't handle, is this code is calling into a user defined ICustomQueryInterface.GetInterface(). The user could cast any int to CustomQueryInterfaceResult and then the above logic is flawed.

[shushanhf]

Is this on a Release or Debug/Checked build?

On Debug build on the LoongArch64-linux with clang-13 and arm64 linux with clang-8.
I tested it on AMD64-linux that is also failed when building the coreclr.

[AaronRobinsonMSFT]

Thank you.