dotest.py has migrated from accepting multiple arch'es to test for, to only taking one on llvm.org.  Update some code on the github dotest.py that was still assuming that archs was an array.
dotest.py has migrated from accepting multiple arch'es to test for,
to only taking one on llvm.org.  Update some code on the github
dotest.py that was still assuming that archs was an array.

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb