With some trepidation I download the "already patched saboteur.exe" from above
(i.e., Saboteur_Fix.7z (mega.nz/#!gA1mBZLR!qr7lUxuaNJr_-Ietgw9ARxZ_4j7_TRUp6UFdaNcf95M) - already patched Saboteur.exe)
It was the exact same size (in bytes) as my existing saboteur.exe from GOG. I then scanned the patched one with two different security programs and they didn't find anything. Then I used CompareIt to compare the two files. As mentioned above there is just the one byte difference.
So crossing my fingers I ran it and ... it works! It runs really well on my 12 core system.
I can confirm that the patched Saboteur.exe and the original Saboteur.exe differ at only one byte value. I just checked myself with HxD.
The value is at address 0x9F56D0 in the file and the value of the byte is changed from 0x76 to 0xEB.
And I can also confirm that this works for me as well with all cores of my CPU enabled.
CPU: Core i7 5930K,
OS: Windows 10 x64 (build 1703, all updates), NVidia GeForce GTX 1060 6GB.
It's such a relief too, since I had set my BIOS to disable 2 out of the 6 cores of my CPU in order to run this game, a few months ago, and I had forgot I was still using my PC with that configuration.
Thank you to own3mall and I guess, JackFuste.
Ideally JackFuste would get in touch with GOG to explain how he resolved this.
I think a lot of people will be skeptical to try an unofficial patch that is distributed from mega.nz, and it's really a shame, because this time, this fix actually works!
Edit: I guess one could try to just do the switch of the byte as I explain above. You really need a hex editor like HxD and you should be good to go!