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-core/config-schema.json

@@ -194,6 +194,13 @@
       "name": "Register '$' prefix",
       "description": "Display MIPS register names with a '$' prefix."
     },
+    {
+      "id": "ppc.calculatePoolRelocations",
+      "type": "boolean",
+      "default": true,
+      "name": "Calculate pooled data references",
+      "description": "Display pooled data references in functions as fake relocations."
+    },
     {
       "id": "x86.formatter",
       "type": "choice",
@@ -253,6 +260,13 @@
         "mips.registerPrefix"
       ]
     },
+    {
+      "id": "ppc",
+      "name": "PPC",
+      "properties": [
+        "ppc.calculatePoolRelocations"
+      ]
+    },
     {
       "id": "x86",
       "name": "x86",