Spinlock instead of Mutex

[QueensGambit]

This PR integrates a spinlock as a replacement of mutex for Node.h
The memory consumption is almost identical.
Leads to 17.73 +/- 17.05 Elo improvement in chess.

Also adds if (numPhases > 1) { check in searchthread.cpp

File: /data/SL/spinlock_optimized_v3.pgn

Name                        :  Games                 Elo    Pts   Pts%   Win  Loss  Draw  Tf  Sc
ClassicAra_master           :   1000   -17.73 +/-  17.05  474.5   47.5   288   339   373   0   0
ClassicAra_spinlock         :   1000    17.73 +/-  17.05  525.5   52.5   339   288   373   0   0

Name                        :  W_win  B_win   Draw
ClassicAra_master           :    126    162    373
ClassicAra_spinlock         :    153    186    373


Name                        :   Wapc     Sd
ClassicAra_master           :     94     35
ClassicAra_spinlock         :     99     40

Finished games   : 1000
White wins       : 279 (27.9%)
Black wins       : 348 (34.8%)
Draws            : 746 (74.6%)
Unfinished games : 0 (0.0%)

Tf = time forfeit
Sc = stalled connection
Wapc = win average ply count, lower is better
Sd = standard deviation