[llvm] [Object] Provide operator< for ELFSymbolRef (PR #89861)

[Amir Ayupov via llvm-commits]

aaupov wrote:

> Thanks for the explanation about why this whole thing is important, the new commit message is certainly clearer. I think the last sentence of the description would be clearer saying: "For ELFSymbolRef a specialized operator< can be used instead to produce consistent ordering regardless of endianness by comparing the symbol table index and symbol index fields separately."

Thanks, updated.

> 
> One other thing: does `DataRefImpl` have an `operator>`? If so, you'll need that here too as otherwise two ELFSymbolRefs will not have inconsistent orderings based on which comparison operator is being used.

No, it doesn't: https://github.com/llvm/llvm-project/blob/2d09ac4037415ab0044ad508aae2ff8b2559a9d8/llvm/include/llvm/Object/SymbolicFile.h#L53-L67

https://github.com/llvm/llvm-project/pull/89861