[gn] Switch linux64 debug and internal snapshot to gn

gni/v8.gni

 # Copyright 2016 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.
 
 import("//build/config/v8_target_cpu.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 declare_args() {
+  # Indicate if valgrind was fetched as a custom deps to make it available on
+  # swarming.
+  v8_has_valgrind = false
+
   # Turns on compiler optimizations in V8 in Debug build.
   v8_optimized_debug = true
 
   # Enable the snapshot feature, for fast context creation.
   # http://v8project.blogspot.com/2015/09/custom-startup-snapshots.html
   v8_use_snapshot = true
 
   # Use external files for startup data blobs:
   # the JS builtins sources and the start snapshot.
   v8_use_external_startup_data = !is_ios
@@ skipping 51 matching lines @@
 }
 
 template("v8_component") {
   component(target_name) {
     forward_variables_from(invoker, "*", [ "configs" ])
     configs += invoker.configs
     configs -= remove_configs
     configs += add_configs
   }
 }