Generate Qsearch checks only at depth 0

An old idea retested at SPRT(0, 3) with 60+0.05 TC:
LLR: 2.95 (-2.94,2.94) [0.00,3.00]
Total: 98872 W: 15549 L: 15123 D: 68200

This is a very small elo increase patch so it really
stresses the limits of fishtest.

bench: 8596156
Add support for PPC 64bit on Linux

In particular Debian Linux-3.9.8-1- PPC64

No functional change.
Stockfish DD

Stockfish bench signature is: 8596156
Merge tag 'sf_dd'

Conflicts:
	src/uci.cpp