[thunderbird-lightning/f18] (3 commits) ...Remove _arch because _arch returns i386 while we need i686

[Jan Horak]

Summary of changes:

  69c2458... Added libvpx to buildrequires (*)
  c919185... Temp override because of internal compiler error - case may (*)
  17afcd5... Remove _arch because _arch returns i386 while we need i686 (*)

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