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

[Amir Ayupov via llvm-commits]

aaupov wrote:

> > > Also, is there a reason you provide `<` but not `==`? I note that `DataRefImpl` has both.
> > 
> > 
> > DataRefImpl's `operator==` is good enough for comparison.
> 
> Why is DataRefImpl's `operator<` not good enough when the `operator==` is?

Sorry, I've made the commit message more clear. DataRefImpl's `operator<` uses std::memcmp whose result is endianness-dependent (as shown by added test), which is exactly the issue addressed by a custom `operator<` for ELFSymbolRefs. 
`operator==` also uses std::memcmp but equality is invariant wrt endianness.

> 
> Also, please try to avoid force pushes in active reviews, per the LLVM guidelines. If rebasing is necessary, consider merging `main` into your branch instead.

Noted, thank you.

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