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.
Resolves #222