[LV] Add scalable vector test showing incorrect min-trip count check.

The test shows a case where the minimum trip count check incorrectly
only checks the minimum profitable trip count computed due to runtime
checks. This is incorrect for scalable VFs, because the VF * UF may
exceed the minimum profitable trip count for vscale > 1.

This is the likely reason for
https://lab.llvm.org/buildbot/#/builders/197/builds/2262 failing.