ntdll: Add a stub implementation for RtlDllShutdownInProgress.

[Robert Shearman]

Mike McCormack wrote:
> +NTSTATUS WINAPI RtlDllShutdownInProgress(void)
> +{
> +    FIXME("\n");
> +    return STATUS_SUCCESS;
> +}

For undocumented functions like this, you should add a test case.

-- 
Rob Shearman