[sane-backends/f14/master] (2 commits) ...build mustek_usb2 backend again, enable use of libpthread (#603321)

[Nils Philippsen]

Summary of changes:

  8bd23f1... let sane-backends require arch-specific version/release of  (*)
  e7b660e... build mustek_usb2 backend again, enable use of libpthread ( (*)

(*) This commit already existed in another branch; no separate mail sent