Fix Windows x86 u64 popcount

Author: onalante-ebay

include/xsimd/types/xsimd_bit.hpp

@@ -81,7 +81,11 @@ namespace xsimd
 #elif XSIMD_HAS_BUILTIN(__builtin_popcount)
                 return __builtin_popcount((unsigned int)x) + __builtin_popcount((unsigned int)(x >> 32));
 #elif defined(_MSC_VER)
+#ifdef _M_X64
                 return (int)__popcnt64(x);
+#else
+                return (int)(__popcnt((unsigned int)x) + __popcnt((unsigned int)(x >> 32)));
+#endif
 #else
                 // https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
                 x = x - ((x >> 1) & (T) ~(T)0 / 3);