I compiled the code with minor changes on my M3 Macbook Air and it found the 19186 unique solutions in about 3hrs 15min, so ~9.2X speedup (over the 30hrs stated in the post). Would indeed be interesting to see how fast you can go with some optimization.

EDIT: I forgot to add -O3 the first time, with that the time to 19186 drops to under and hour, so over 30X speedup.