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/src/arch/mod.rs

@@ -10,8 +10,8 @@ use crate::{
         DiffObjConfig,
     },
     obj::{
-        InstructionArg, Object, ParsedInstruction, RelocationFlags, ResolvedInstructionRef,
-        ScannedInstruction, SymbolFlagSet, SymbolKind,
+        InstructionArg, Object, ParsedInstruction, Relocation, RelocationFlags,
+        ResolvedInstructionRef, ScannedInstruction, Symbol, SymbolFlagSet, SymbolKind,
     },
     util::ReallySigned,
 };
@@ -212,6 +212,17 @@ pub trait Arch: Send + Sync + Debug {
         cb: &mut dyn FnMut(InstructionPart) -> Result<()>,
     ) -> Result<()>;
 
+    /// Generate a list of fake relocations from the given code that represent pooled data accesses.
+    fn generate_pooled_relocations(
+        &self,
+        _address: u64,
+        _code: &[u8],
+        _relocations: &[Relocation],
+        _symbols: &[Symbol],
+    ) -> Vec<Relocation> {
+        Vec::new()
+    }
+
     fn implcit_addend(
         &self,
         file: &object::File<'_>,