Fix Windows

Author: onalante-ebay

include/xsimd/types/xsimd_bit.hpp

@@ -113,7 +113,7 @@ namespace xsimd
 #elif defined(_MSC_VER)
                 unsigned long index;
                 _BitScanReverse(&index, (unsigned long)x);
-                return index;
+                return sizeof(T) * CHAR_BIT - index - 1;
 #else
                 x |= x >> 1;
                 x |= x >> 2;
@@ -137,7 +137,7 @@ namespace xsimd
 #elif defined(_MSC_VER) && defined(_M_X64)
                 unsigned long index;
                 _BitScanReverse64(&index, (unsigned long long)x);
-                return index;
+                return sizeof(T) * CHAR_BIT - index - 1;
 #else
                 x |= x >> 1;
                 x |= x >> 2;