[lld] [ELF, RISCV] Fix oscillation due to call relaxation (PR #142899)

[via llvm-commits]

LukeZhuang wrote:

Hi Fangrui, just curious that the `4` in `pass < 4 ? 6 : cur - delta` works as a threshold, right? If pass less than 4, everything just happens as before, otherwise you restrict the relaxation process of call.
If so, why is that "4", would it be too conservative?

https://github.com/llvm/llvm-project/pull/142899