[WebAssembly] Remove StackPointerGlobal member variable from the driver.

[ruiu]

Summary

Since InputGlobal makes a copy of a given object, we can use a temporary
object allocated on the stack here.

[sbc100]

Still good to go?

lld/wasm/Driver.cpp

 public:
   void link(ArrayRef<const char *> ArgsArr);
 
 private:
   void createFiles(opt::InputArgList &Args);
   void addFile(StringRef Path);
   void addLibrary(StringRef Name);
   std::vector<InputFile *> Files;
-  llvm::wasm::WasmGlobal StackPointerGlobal;
 };
 } // anonymous namespace
 
 bool lld::wasm::link(ArrayRef<const char *> Args, bool CanExitEarly,
                      raw_ostream &Error) {
   errorHandler().LogName = Args[0];
   errorHandler().ErrorOS = &Error;
   errorHandler().ColorDiagnostics = Error.has_colors();
void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   }
 
   Symbol *EntrySym = nullptr;
   if (!Config->Relocatable) {
     // Can't export the SP right now because it's mutable, and mutable
     // globals aren't yet supported in the official binary format.
     // TODO(sbc): Remove WASM_SYMBOL_VISIBILITY_HIDDEN if/when the
     // "mutable global" proposal is accepted.
-    StackPointerGlobal.Type = {WASM_TYPE_I32, true};
-    StackPointerGlobal.InitExpr.Value.Int32 = 0;
-    StackPointerGlobal.InitExpr.Opcode = WASM_OPCODE_I32_CONST;
-    InputGlobal *StackPointer = make<InputGlobal>(StackPointerGlobal);
+    llvm::wasm::WasmGlobal Global;
+    Global.Type = {WASM_TYPE_I32, true};
+    Global.InitExpr.Value.Int32 = 0;
+    Global.InitExpr.Opcode = WASM_OPCODE_I32_CONST;
+    InputGlobal *StackPointer = make<InputGlobal>(Global);
     StackPointer->Live = true;
 
     static WasmSignature NullSignature = {{}, WASM_TYPE_NORESULT};
     // Add synthetic symbols before any others
     WasmSym::CallCtors = Symtab->addSyntheticFunction(
         "__wasm_call_ctors", &NullSignature, WASM_SYMBOL_VISIBILITY_HIDDEN);
     WasmSym::StackPointer = Symtab->addSyntheticGlobal(
         "__stack_pointer", WASM_SYMBOL_VISIBILITY_HIDDEN, StackPointer);