Construct and propagate the argument to xcodebuild's -sdk option

Change-Id: I810ea99f61c47da62f2489d5176f6fbb779134a9
Pass -sdk option

Change-Id: I694d90e2cfca2b4b68a33df0d3912c2492563d28
Set VALID_ARCHS equal to ARCHS

Change-Id: Ief7d3b09cb68eb2abdb99ebc9cfac7f71cd1476e