[dxgi] Report D3D10 support only when DXVK_FAKE_DX10_SUPPORT is set

Should fix a regression in Assassin's Creed 4: Black Flag.

README.md

@@ -80,7 +80,8 @@ The following environment variables can be used for **debugging** purposes.
 - `DXVK_DEBUG_LAYERS=1` Enables Vulkan debug layers. Highly recommended for troubleshooting rendering issues and driver crashes. Requires the Vulkan SDK to be installed and set up within the wine prefix (`winetricks vulkansdk`).
 - `DXVK_CUSTOM_VENDOR_ID=<ID>` Specifies a custom PCI vendor ID
 - `DXVK_CUSTOM_DEVICE_ID=<ID>` Specifies a custom PCI device ID
-- `DXVK_LOG_LEVEL=none|error|warn|info|debug` Controls message logging.
+- `DXVK_LOG_LEVEL=none|error|warn|info|debug` Controls message logging
+- `DXVK_FAKE_DX10_SUPPORT=1` Advertizes support for D3D10 interfaces
 
 ## Troubleshooting
 DXVK requires threading support from your mingw-w64 build environment. If you

src/dxgi/dxgi_adapter.cpp

@@ -60,7 +60,9 @@ namespace dxvk {
     if (InterfaceName == __uuidof(ID3D10Device)
      || InterfaceName == __uuidof(ID3D10Device1)) {
       Logger::warn("DXGI: CheckInterfaceSupport: No D3D10 support");
-      return S_OK;
+
+      if (env::getEnvVar(L"DXVK_FAKE_DX10_SUPPORT") == "1")
+        return S_OK;
     }
 
     Logger::err("DXGI: CheckInterfaceSupport: Unsupported interface");