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

src/compiler/ast-graph-builder.cc

Index: src/compiler/ast-graph-builder.cc
diff --git a/src/compiler/ast-graph-builder.cc b/src/compiler/ast-graph-builder.cc
index 0f1fb291eb33f5d90c5ef28b989e4d397e34ce5a..188a5134c8a53076249b73ea31675fda7e7e5b4d 100644
--- a/src/compiler/ast-graph-builder.cc
+++ b/src/compiler/ast-graph-builder.cc
@@ -573,7 +573,7 @@ void AstGraphBuilder::CreateGraphBody(bool stack_check) {
   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);