In what way do these &quot;environment subsystems&quot; differ from a user-level library? Linux has a Win32 subsystem, it&#x27;s called &quot;Wine&quot;, and POSIX subsystems called &quot;glibc&quot; and &quot;musl&quot;.<p>Seriously, what makes these &quot;subsystems&quot; different than &quot;libraries&quot;, other than they are shipped with the OS?