Don't use _pext_u64() directly

This intrinsic to call BMI2 PEXT instruction is
defined in immintrin.h. This header should be
included only when USE_PEXT is defined, otherwise
we define _pext_u64 as 0 forcing a nop.

But under some mingw platforms, even if we don't
include the header, immintrin.h gets included
anyhow through an include chain that starts with
STL <algorithm> header. So we end up both defining
_pext_u64 function and at the same time defining
_pext_u64 as 0 leading to a compile error.

The correct solution is of not using _pext_u64 directly.

This patch fixes a compile error with some mingw64
package when compiling with x86-64.

No functional change.

src/types.h

@@ -71,8 +71,9 @@
 
 #if defined(USE_PEXT)
 #  include <immintrin.h> // Header for _pext_u64() intrinsic
+#  define pext(b, m) _pext_u64(b, m)
 #else
-#  define _pext_u64(b, m) (0)
+#  define pext(b, m) (0)
 #endif
 
 #ifdef _MSC_VER