Remove -arch configure option

This option was removed from configure in
qtbase/ba6952b28d17b6b34f65510be645e414fa1ef6a2

  NOTICE: The -arch and -host-arch options are obsolete.

  Qt now detects the target and host architectures based on compiler
  output. Qt will be built using arm for the target architecture
  and i386 for the host architecture (note that these two
  will be the same unless you are cross-compiling).

Change-Id: Ie683623f0069d6a9d05e60ca61ed0d10e996fab0
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>