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

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index a4eae25aedf569b5ac2f44fa8dcc219241fb1e34..5fbec4a79dd978f59012ac70e84bdcd6f5d18719 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -270,9 +270,12 @@ config("compiler") {
         "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",
       ]
     }