cibuildwheel should error out if the same build produces multiple wheels with the same filename

[joerick]

As discussed in #1129, we shouldn't silently overwrite wheels that are produced in the same run that have the same filename, as this implies a misconfiguration.

See #1129 (comment) and #1129 (comment) for further detail.

(alternatively, we could try to cover more wheel overlap cases with the same technique used in our ABI3 wheel support. See #1129 (comment) for an idea on this)