There are some users of that tri_comparator which are also
converted to strong_ordering. Most of the code using those
is, in turn, already handling return values interchangeably.
The bound_view::tri_compare, which's used by the guy, is
still returning int.
tests: unit(dev)
* xemul/br-position-tri-compare:
code: Relax position_in_partition::tri_compare users
position_in_partition: Convert tri_compare to strong_ordering
test: Convert clustering_fragment_summary::tri_cmp to strong_ordering
repair: Convert repair_sync_boundary::tri_compare to strong_ordering
view: Don't expect int from position_in_partition::tri_compare
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