Let prefetch to be enabled by default on Windows

When compiling with MSVC we don't use the Makefile
so tweak a bit the Makefile to allow to let prefetch
in by default so that it works under Windows.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/Makefile

@@ -64,6 +64,7 @@ OBJS = application.o bitboard.o pawns.o material.o endgame.o evaluate.o main.o \
 ### 2.1. General
 debug = no
 optimize = yes
+no_prefetch = yes
 
 ### 2.2 Architecture specific
 
@@ -278,7 +279,11 @@ endif
 
 ### 3.8 prefetch
 ifeq ($(prefetch),yes)
-	CXXFLAGS += -msse -DUSE_PREFETCH
+	no_prefetch = no
+endif
+
+ifeq ($(no_prefetch),yes)
+	CXXFLAGS += -msse -DNO_PREFETCH
 	DEPENDFLAGS += -msse
 endif
 

src/tt.cpp

@@ -25,7 +25,7 @@
 #include <cassert>
 #include <cmath>
 #include <cstring>
-#if defined(USE_PREFETCH)
+#if !defined(NO_PREFETCH)
 #  include <xmmintrin.h>
 #endif
 
@@ -166,7 +166,7 @@ TTEntry* TranspositionTable::retrieve(const Key posKey) const {
 /// to be loaded from RAM, that can be very slow. When we will
 /// subsequently call retrieve() the TT data will be already
 /// quickly accessible in L1/L2 CPU cache.
-#if !defined(USE_PREFETCH)
+#if defined(NO_PREFETCH)
 void TranspositionTable::prefetch(const Key) const {}
 #else