[lld] [lld] Merge GOT entries for symbols (PR #131630)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> * a Section A1, with a relocation on a symbol S1, where S1 is at offset K in section B1.
> * a Section A2, with a relocation on a symbol S2, where S2 is at offset K in section B2.
>
> [...] But in looking into it more, I think something like this could work: [gist.github.com/jyknight/20776f8a2a87b3dbababeca7d9e001fa](https://gist.github.com/jyknight/20776f8a2a87b3dbababeca7d9e001fa)

Thanks for the analysis. I think this reasoning captures the core issue. could you please create a pull request with a corresponding test case? (Also test `.got` size) Modifying `file->getMutableSymbols();` resembles `redirectSymbols` and makes the relocation scanning pass entirely skip the folded symbols, which I think is the right direction.

https://github.com/llvm/llvm-project/pull/131630