[llvm] [llvm][AArch64] Improve the cost model for i128 div's (PR #107306)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

We tend to use 10 as the cost of a libcall. Does what you are doing need to be more precise than that?

It might be worth using `size > 64`. For larger sizes the codegen is horrendous, but giving it a higher cost sounds at least more correct!  It could be 10 * type legalization cost or something like it.

Otherwise this sounds good to me. Let me know what you think.

https://github.com/llvm/llvm-project/pull/107306