[llvm] [LoopVectorize] Price vector library variants in getVectorCallCost (PR #202085)

[via llvm-commits]

seantalts wrote:

> this needs a test that exercises the code path

Thanks for looking! I added a test. The update_test_checks tool added a LOT of assertions, not sure if it's standard to leave all of them in.

https://github.com/llvm/llvm-project/pull/202085