[lld] [WASM] wasm-ld: split up __wasm_apply_data_relocs (PR #129007)

[via llvm-commits]

================
@@ -299,6 +299,8 @@ void FunctionSection::writeBody() {
 void FunctionSection::addFunction(InputFunction *func) {
   if (!func->live)
     return;
+  if (func->hasFunctionIndex())
+    return;
----------------
dmjio wrote:

Maybe `assert(!hasFunctionIndex());` was being triggered in `setFunctionIndex`, and `if (func->hasFunctionIndex()) return;` was introduced to keep program termination from occurring.

```c++
void InputFunction::setFunctionIndex(uint32_t index) {                                                                                                 
  LLVM_DEBUG(dbgs() << "InputFunction::setFunctionIndex: " << name << " -> "                                                                           
                    << index << "\n");                                                                                                                 
  assert(!hasFunctionIndex());                                                                                                                         
  functionIndex = index;                                                                                                                               
}  
```

https://github.com/llvm/llvm-project/pull/129007