Add ability to disable performance-sensitive relaxed atomic operations at compile time
Adds a `RelaxedAtomic` wrapper around either `T` or `std::atomic<T>` and `USE_SLOPPY_ATOMICS` preprocessor define. The intent of this flag is to allow easy disabling of atomics on WASM, where even relaxed atomics are expensive because all atomics have `seq_cst` semantics.
Passed non regression STC
LLR: 2.99 (-2.94,2.94) <-1.75,0.25>
Total: 50624 W: 12976 L: 12776 D: 24872
Ptnml(0-2): 112, 5445, 14005, 5631, 119
https://tests.stockfishchess.org/tests/view/6a1f690e818cacc1db0ad2c7
Passed non-regression STC SMP
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 163696 W: 41514 L: 41438 D: 80744
Ptnml(0-2): 162, 18272, 44904, 18348, 162
https://tests.stockfishchess.org/tests/view/6a21fb97351b79f679cc44b3
Using this class for the TT also allows us to remove the TSAN suppressions, since the UB is fixed.
closes https://github.com/official-stockfish/Stockfish/pull/6877
No functional change