[llvm] CostModel/RISCV: add test for ctpop, with/without ZVBB (PR #67013)

[Philip Reames via llvm-commits]

preames wrote:

We already have coverage for ctpop in test/Analysis/CostModel/RISCV/int-bit-manip.ll.  You don't need to duplicate coverage.  You should add an extract check line and appropriate prefixes to highlight the ZVBB differences.

https://github.com/llvm/llvm-project/pull/67013