[TurboFan] Avoid Gcc compilation fail by Initializing rest_index variable.

src/compiler/ast-graph-builder.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/ast-graph-builder.h"
 
 #include "src/ast/scopes.h"
 #include "src/compiler.h"
 #include "src/compiler/ast-loop-assignment-analyzer.h"
 #include "src/compiler/control-builders.h"
@@ skipping 555 matching lines @@
 }
 
 
 void AstGraphBuilder::CreateGraphBody(bool stack_check) {
   DeclarationScope* scope = info()->scope();
 
   // Build the arguments object if it is used.
   BuildArgumentsObject(scope->arguments());
 
   // Build rest arguments array if it is used.
-  int rest_index;
+  int rest_index = 0;
   Variable* rest_parameter = scope->rest_parameter(&rest_index);
   BuildRestArgumentsArray(rest_parameter, rest_index);
 
   // Build assignment to {.this_function} variable if it is used.
   BuildThisFunctionVariable(scope->this_function_var());
 
   // Build assignment to {new.target} variable if it is used.
   BuildNewTargetVariable(scope->new_target_var());
 
   // Emit tracing call if requested to do so.
@@ skipping 3738 matching lines @@
     // Phi does not exist yet, introduce one.
     value = NewPhi(inputs, value, control);
     value->ReplaceInput(inputs - 1, other);
   }
   return value;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8