Avoid testing multiple bits in CPUID feature checks

[randombit]

For whatever reason both GCC and Clang generate quite terrible code in this case. Instead avoid the problem by never setting a bit if one of the dependency bits is missing, for example on a (hypothetical) core with AES-NI but SSSE3, just avoid setting AES-NI bit in the first place.

[coveralls]

coverage: 91.269% (+0.004%) from 91.265% when pulling a9c1f286540a7a5ed48821adcf9d11e3084bf822 on jack/cpuid-bit-gate into 35573b38503b5e73caf30e9dec217bbea2a92725 on master.