pass ONLY_ACTIVE_ARCH=NO to xctool, hopefully this fixes `make test`

I don't fully understand _why_ this is needed.  I think it's a
shortcoming in xctool, but we don't have it figured out yet.

I find I have to add this whenever I'm running application tests.
Merge pull request #33 from fpotter/fix-make-test

pass ONLY_ACTIVE_ARCH=NO to xctool, hopefully this fixes `make test`