[lld] [LLD][RISCV][Zicfilp] Generate unlabeled landing pad-style PLT (PR #145461)

[Piyou Chen via llvm-commits]

BeMg wrote:

Update:

1. Merge the lpad code and non-lpad code in `writePlt` and `writePltHeader`
2. Refine the comment
3. Replace the 0 with `X_X0`
4. use `ctx.arg.wordsize` instead `ctx.arg.is64 ? 8 : 4`

https://github.com/llvm/llvm-project/pull/145461