Do not compile POPCNT if NO_POPCNT is defined

Do not compile POPCNT if NO_POPCNT is defined

Also rename DISABLE_POPCNT_SUPPORT in NO_POPCNT and simplify a bit
the macro logic.

Always define a __popcnt64()or _mm_popcnt_u64() template, if the proper
function with the same name is defined in the intrinsics header, then it
will be choosen as first otherwise we fall back on the dummy template
that is never called at runtime anyway because cpu_has_popcnt() returns
false.

This fixes the compile error reported by Jim.

No functional change.

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