patch from chinmaygarde@ to make progress on mac, ios.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium 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/android/config.gni")
 import("//build/config/chrome_build.gni")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
@@ skipping 252 matching lines @@
       common_mac_flags += [
         "-arch",
         "x86_64",
       ]
     } else if (current_cpu == "x86") {
       common_mac_flags += [
         "-arch",
         "i386",
       ]
     } else if (current_cpu == "arm") {
+      # TODO(GYP): we may need to distinguish between "arm64", "armv7",
+      # and "armv7s" for iOS, and hence need multiple current_cpu values
+      # rather than just "arm".
       common_mac_flags += [
         "-arch",
-        "armv7",
+        "arm64",
       ]
     }
 
     cflags += common_mac_flags
 
     # Without this, the constructors and destructors of a C++ object inside
     # an Objective C struct won't be called, which is very bad.
     cflags_objcc += [ "-fobjc-call-cxx-cdtors" ]
 
     cflags_c += [ "-std=c99" ]
@@ skipping 995 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }