Select among binaries based upon x86 microarchitecture support

 Pick an executable based on CPU capabilities.
 .
 Call subarch-select with argument pairs that list CPU features
 (as in /proc/cpuinfo "flags"), and a path to execute if the flags are all
 matched. The first set of flags that match the system capabilities will select
 the given path. Arguments to the program should be passed after "--".
 .
 Also supports the x86-64 microarchitectures: x86-64-v2, x86-64-v3, v86-64-v4