Fix "Build Active Architecture Only" build setting for iOS target

The `ONLY_ACTIVE_ARCH` ("Build Active Architecture Only") build setting should be set to `NO` for iOS targets, as per jspahrsummers/xcconfigs@ae4762d:

> If a library only built one architecture, then was used in a parent project that wanted all of them, things asplode.

This should *partially* fix Quick/Quick#111, i.e. phantom "unresolved identifier" errors.