Cycles/Optix: Add CYCLES_OPTIX_TEST override

This works similarly to the CYCLES_OPENCL_TEST
environment variable to allow testing on unsupported
hardware.

Note: like the OPENCL test override, this is
for *testing* only and bug reports on unsupported
hardware will *not* be accepted at this point in
time.

intern/cycles/device/device_optix.cpp

@@ -1558,7 +1558,7 @@ void device_optix_info(vector<DeviceInfo> &devices)
     }
 
     // Only add devices with RTX support
-    if (rtcore_version == 0)
+    if (rtcore_version == 0 && !getenv("CYCLES_OPTIX_TEST"))
       it = cuda_devices.erase(it);
     else
       ++it;