Yes I have run the leaktest, It seems that file should have been in a temp folder, but it is definitely in system32. The Threatexpert reports show that it is the same file, not just one named the same, so that is strange.
I have neither clt.exe or drivers.sys in system32 or anywhere else now.
I confirmed that dll.dll is is required for Injection: CreateRemoteThread PoC of CLT testsuite version 188.8.131.52.
If that test is failed the dll.dll will be copied in system32 folder, however it will deleted after the result is provided.
Please test the CLT version you got again to confirm this behaviour.
If still dll.dll is not deleted please report your CLT version too.
I downloaded and ran the tests now, as I had not kept CLT before. When I allowed the tests the dll.dll was removed from system32 as you said and all were failed. I see that file is in the clt folder also.
That threatexpert report lead to the IE windows showing Comodo which the test opens.
I think I had the old version of the tests before, so maybe that left the file behind.
One of the way to spot malware when throubleshooting a PC is the name.
A commmon occurence is that the names are typos of legitimate executable or system services.
In some case have some obscure or generic names.
Often the executable filename hints at the software or the task carried by that component.
In this case I guess that file was named dll.dll because the PoC involved a mock-dll to carry the leaktest.