[llvm] [RISCV] Teach RISCVInsertVSETVLI to work without LiveIntervals (PR #93796)

[Luke Lau via llvm-commits]

lukel97 wrote:

Mentioning this as an alternative fix for the crash in #93587, we could also try running the remove unreachable machine block pass at O0 to keep LiveIntervalsAnalysis happy. 

https://github.com/llvm/llvm-project/pull/93796