[lib/LinuxVersion] multiple fixes

• remove fancy but broken static LinuxVersion object.
  This means each usage of a EMPER_LINUX_* macro results in a syscall.
  But I think this is worth it when the result is a sound program.
  Users of those macros should store the result of the comparison anyway.
• fix that we skipped parsing the last part of a version string
• add a test for LinuxVersion
• IO_MUST_INVALIDATE_BROKEN_CHAIN can still be const