[lld] [lld-macho] Fix compatibility between --icf=safe_thunks and --keep-icf-stabs (PR #116687)

[Kyungwoo Lee via llvm-commits]

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@@ -481,6 +481,33 @@ void macho::markAddrSigSymbols() {
   }
 }
 
+// Given a symbol that was folded into a thunk, return the symbol pointing to
+// the actual body of the function. We use this approach rather than storing the
+// needed info in the Defined itself in order to minimize memory usage.
+Defined *macho::getBodyForThunkFoldedSym(Defined *foldedSym) {
+  assert(isa<ConcatInputSection>(foldedSym->originalIsec) &&
+         "thunk-folded ICF symbol expected to be on a ConcatInputSection");
+  // foldedSec is the InputSection that was marked as deleted upon fold
+  ConcatInputSection *foldedSec =
+      cast<ConcatInputSection>(foldedSym->originalIsec);
+
+  // thunkBody is the actual live thunk, containing the code that branches to
+  // the actual body of the function.
+  InputSection *thunkBody = foldedSec->replacement;
+
+  // the actual (merged) body of the function that the thunk jumps to. This will
----------------
kyulee-com wrote:

```suggestion
  // The actual (merged) body of the function that the thunk jumps to. This will
```

https://github.com/llvm/llvm-project/pull/116687