PPC: Reimplement pooled data reference calculation (#167)

* PPC: Calculate pooled relocations

Reimplements #140

The relocations are now generated when the object is first read in `parse`, right after the real relocations are read.

`resolve_relocation` was changed to take `obj.symbols` instead of `obj` as an argument, because `obj` itself doesn't exist yet at the time the relocations are being read.

* Improve readability of PPC pool relocs code

* Fix regression causing extern pool relocs to be ignored

* Fix showing incorrect diff when diffing weak stripped symbol with an addend

This is a regression that was introduced by #158 diffing addends in addition to symbol names. But it's not really a bug in that PR, rather it seems like I simply never added the offset into the addend when creating a fake pool relocation for an extern symbol. So this commit fixes that root issue instead.

* Add PPC "Calculate pooled data references" option

* Fix objdiff-wasm compilation errors

* Update PPC test snapshots

objdiff-gui/src/views/data_diff.rs

@@ -32,7 +32,7 @@ fn data_row_hover(obj: &Object, diffs: &[(DataDiff, Vec<DataRelocationDiff>)]) -
         // TODO: Change hover text color depending on Insert/Delete/Replace kind
         // let color = get_color_for_diff_kind(reloc_diff.kind, appearance);
 
-        let reloc = resolve_relocation(obj, reloc);
+        let reloc = resolve_relocation(&obj.symbols, reloc);
         out.append(&mut relocation_hover(obj, reloc));
     }
     out
@@ -55,7 +55,7 @@ fn data_row_context(
         }
         prev_reloc = Some(reloc);
 
-        let reloc = resolve_relocation(obj, reloc);
+        let reloc = resolve_relocation(&obj.symbols, reloc);
         out.append(&mut relocation_context(obj, reloc, None));
     }
     out