[WebAssembly] Use make<> rather then make_unique<>. NFC.

[sbc100]

Summary

lld uses an arena allocator to one of allocations
like these can just use make<>.

[sbc100]

Is my rational correct here? Based on your feedback from my other change it seems like this should be preferred?

[ruiu]

LGTM

wasm/Writer.cpp

private:
   std::vector<const FunctionSymbol *> IndirectFunctions;
   std::vector<WasmInitFunc> InitFunctions;
 
   // Elements that are used to construct the final output
   std::string Header;
   std::vector<OutputSection *> OutputSections;
 
   std::unique_ptr<FileOutputBuffer> Buffer;
-  std::unique_ptr<SyntheticFunction> CtorFunction;
   std::string CtorFunctionBody;
 
   std::vector<OutputSegment *> Segments;
   llvm::SmallDenseMap<StringRef, OutputSegment *> SegmentMap;
 };
 
 } // anonymous namespace
 
void Writer::createCtorFunction() {
   // Once we know the size of the body we can create the final function body
   raw_string_ostream OS(CtorFunctionBody);
   writeUleb128(OS, FunctionBody.size(), "function size");
   OS.flush();
   CtorFunctionBody += FunctionBody;
   ArrayRef<uint8_t> BodyArray(
       reinterpret_cast<const uint8_t *>(CtorFunctionBody.data()),
       CtorFunctionBody.size());
-  CtorFunction = llvm::make_unique<SyntheticFunction>(
-      Signature, BodyArray, WasmSym::CallCtors->getName());
-  CtorFunction->setOutputIndex(FunctionIndex);
-  InputFunctions.emplace_back(CtorFunction.get());
+  SyntheticFunction *F = make<SyntheticFunction>(Signature, BodyArray,
+                                                 WasmSym::CallCtors->getName());
+  F->setOutputIndex(FunctionIndex);
+  InputFunctions.emplace_back(F);
 }
 
 // Populate InitFunctions vector with init functions from all input objects.
 // This is then used either when creating the output linking section or to
 // synthesize the "__wasm_call_ctors" function.
 void Writer::calculateInitFunctions() {
   for (ObjFile *File : Symtab->ObjectFiles) {
     const WasmLinkingData &L = File->getWasmObj()->linkingData();