Option to enable AVX-512

[maximmasiutin]

Please consider adding an option to enable AVX-512 support in Fishtest. This option could be implemented as a command-line parameter, an environment variable, or both. Currently, AVX-512 is disabled in Fishtest to prevent potential CPU frequency drops that can occur with AVX-512-intensive code.

Even though CPUs may support AVX-512, Fishtest does not compile Stockfish with AVX-512 instructions to avoid these frequency drops, which can negatively impact overall performance. However, my CPU has two FMA (Fused Multiply-Add) units per core, and it does not experience frequency reductions when only a few threads utilize AVX-512 instructions. By allocating only a few threads to Fishtest, the CPU frequency remains stable, allowing me to benefit from the enhanced performance of AVX-512.

Therefore, having an option to enable AVX-512 would be beneficial. If you agree with this suggestion, I would be happy to submit a pull request to implement this feature.