[ELF] Detect convergence of output section addresses

Some linker scripts don't converge. https://reviews.llvm.org/D66279
("[ELF] Make LinkerScript::assignAddresses iterative") detected
convergence of symbol assignments.

This patch detects convergence of output section addresses. While input
sections might also have convergence issues, they are less common as
expressions that could cause convergence issues typically involve output
sections and symbol assignments.

GNU ld has an error `non constant or forward reference address expression for section` that
correctly rejects
```
SECTIONS {
  .text ADDR(.data)+0x1000 : { *(.text) }
  .data : { *(.data) }
}
```

but not the following variant:
```
SECTIONS {
  .text foo : { *(.text) }
  .data : { *(.data) }
  foo = ADDR(.data)+0x1000;
}
```

Our approach consistently rejects both cases.

Link: https://discourse.llvm.org/t/lld-and-layout-convergence/79232

Pull Request: https://github.com/llvm/llvm-project/pull/93888