[gn] Port more build flags for gn

build_overrides/v8.gni

 # Copyright 2015 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/features.gni")
 import("//build/config/ui.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
 }
 
+declare_args() {
+  # V8 generates code for this architecture.

[Michael Achenbach, 2016/05/17 15:15:44]

This adds the standalone default from gyp here:
https://code.google.com/p/chromium/codesearch#chromium/src/v8/gypfiles/standa...

+  v8_target_arch = target_cpu
+}
+
+if (((v8_target_arch == "ia32" ||

[Michael Achenbach, 2016/05/17 15:15:44]

This ports 1:1 the following:
https://code.google.com/p/chromium/codesearch#chromium/src/v8/gypfiles/standa...

+      v8_target_arch == "x64" ||
+      v8_target_arch=="x87") &&
+     (is_linux || is_mac)) ||
+    (v8_target_arch == "ppc64" && is_linux)) {
+  v8_enable_gdbjit = true
+}
+
+v8_imminent_deprecation_warnings = true

[Michael Achenbach, 2016/05/17 15:15:44]

This ports:
https://code.google.com/p/chromium/codesearch#chromium/src/v8/gypfiles/standa...

 v8_optimized_debug = false
 v8_extra_library_files = []
 v8_experimental_extra_library_files = []