[d3d11] Stub out OpenSharedResourceGeneric on non-Windows

src/d3d11/d3d11_device.cpp

@@ -2256,6 +2256,7 @@ namespace dxvk {
     if (ppResource == nullptr)
       return S_FALSE;
 
+#ifdef _WIN32
     HANDLE ntHandle = IsKmtHandle ? openKmtHandle(hResource) : hResource;
 
     if (ntHandle == INVALID_HANDLE_VALUE) {
@@ -2298,6 +2299,10 @@ namespace dxvk {
       Logger::err(e.message());
       return E_INVALIDARG;
     }
+#else
+    Logger::warn("D3D11Device::OpenSharedResourceGeneric: Not supported on this platform.");
+    return E_INVALIDARG;
+#endif
   }