Introduce bitcount.h

It will be used for POPCNT intrinsics.

For now no bianry and functional change.

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

src/bitboard.cpp

@@ -35,6 +35,7 @@
 #include <iostream>
 
 #include "bitboard.h"
+#include "bitcount.h"
 #include "direction.h"
 
 
@@ -460,7 +461,7 @@ namespace {
 
 
   Bitboard index_to_bitboard(int index, Bitboard mask) {
-    int i, j, bits = count_1s(mask);
+    int i, j, bits = count_1s<false>(mask);
     Bitboard result = 0ULL;
     for(i = 0; i < bits; i++) {
       j = pop_1st_bit(&mask);