Fix for compile error when no AVX2 math set

[tillchess]

Line 127 in the Makefile:
CXXFLAGS+=-msse3 -mpopcnt
#CXXFLAGS += -mavx2

[dshawul]

Scorpio needs additional libraries to work with neural networks which are all compiled with AVX2 enabled due to performance reasons, but I guess Scorpio itself canbe be compiled without it. If your machine does not have AVX2, you won't be able to use either NNUE or big NN.

[tillchess]

Right. I noticed it after I wrote the above message.