Simplify release build coding in Makefile

Signed-off-by: Pauli Nieminen <suokkos@gmail.com>
Trust clang to optimize popcnt correctly

Signed-off-by: Pauli Nieminen <suokkos@gmail.com>
Use compiler provided __get_cpuid to avoid issues with pic register

Signed-off-by: Pauli Nieminen <suokkos@gmail.com>