Fix android_arm64 target for experimental ndk

build/android.gypi

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 33 matching lines @@
         'variables': {
           'android_sysroot': '<(android_toolchain)/sysroot/',
           'android_stlport': '<(android_toolchain)/sources/cxx-stl/stlport/',
         },
         'android_include': '<(android_sysroot)/usr/include',
         'android_lib': '<(android_sysroot)/usr/lib',
         'android_stlport_include': '<(android_stlport)/stlport',
         'android_stlport_libs': '<(android_stlport)/libs',
       }, {
         'variables': {
-          'android_sysroot': '<(android_ndk_root)/platforms/android-9/arch-<(android_target_arch)',
+          'android_sysroot': '<(android_ndk_root)/platforms/android-<(android_target_platform)/arch-<(android_target_arch)',
           'android_stlport': '<(android_ndk_root)/sources/cxx-stl/stlport/',
         },
         'android_include': '<(android_sysroot)/usr/include',
         'android_lib': '<(android_sysroot)/usr/lib',
         'android_stlport_include': '<(android_stlport)/stlport',
         'android_stlport_libs': '<(android_stlport)/libs',
       }],
     ],
     # Enable to use the system stlport, otherwise statically
     # link the NDK one?
@@ skipping 204 matching lines @@
         'ldflags!': [
           '-Wl,-z,noexecstack',
           '-Wl,--gc-sections',
           '-Wl,-O1',
           '-Wl,--as-needed',
         ],
       }],
     ],  # target_conditions
   },  # target_defaults
 }