[RegAlloc] Add coverage leading to revert of pr160765 (#161614)

Essentially what happened is the following series of events: 
1) We rematerialized the vmv.v.x into the loop.
2) As this was the last use of the instruction, we deleted the
   instruction, and removed it from the original live range.
3) We split the live range for the remat.
4) We tried to rematerialize the uses of that split interval, and
   crashed because the assert about the def being available in
   the original live interval does not hold.

0 files changed, 0 insertions, 0 deletions