[LV] Use forced cost once for whole interleave group in legacy costmodel#168270

fhahn wants to merge 1 commit intollvm:mainllvm/llvm-project:mainfrom

fhahn:vplan-cost-forced-instr-cost-interleavefhahn/llvm-project:vplan-cost-forced-instr-cost-interleaveCopy head branch name to clipboard