Dependency resolver should check for features based on the target OS

[ibriano]

Our dependency resolver script is currently checking for a list of things independently of the target OS (with the OS itself being one of those things). In order to avoid false positives and provide a better description of what's available on the current build for each OS, it should first run the compiler specific checks, then detect the OS it's being built for, and from that last detection use a list of things to check that matches the OS.