Minor movegen speed-up

[87flowers]

Small pinner detection speed-up

Test  | minor-perft-opt
Elo   | 3.42 +- 3.16 (95%)
SPRT  | 4.0+0.04s Threads=1 Hash=16MB
LLR   | 2.94 (-2.94, 2.94) [-3.00, 0.00]
Games | N: 16240 W: 4253 L: 4093 D: 7894
Penta | [224, 1836, 3859, 1958, 243]

https://clockworkopenbench.pythonanywhere.com/test/1067/

Bench: 13398527

[TheRealGioviok]

Speedup AND cleanup of intrinsics from position.cpp, very nice.
Edit: check errors in tests.