[lld] [LLD][ELF] add bp-* options in ELF (PR #120514)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> @MaskRay Hey! Made the changes you suggested:
> 
> * used DenseSet to avoid duplicate inputSections
> * cleaned up test suite formatting
> * updated getSymbols to return all defined symbols
> 
> Mind taking another look? Thanks!

I am waiting on the approval of #121729 as a prerequisite. Then the symbol/section representation should be refined.

https://github.com/llvm/llvm-project/pull/120514