Prepares for arm64 cross-build.

tools/gyp/configurations_make.gypi

 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 {
   'variables': {
     'dart_debug_optimization_level%': '2',
   },
   'target_defaults': {
     'configurations': {
@@ skipping 63 matching lines @@
       'Dart_Linux_arm_Base': {
         'abstract': 1,
         'cflags': [
           '-marm',
           '-mfpu=vfp',
           '-Wno-psabi', # suppresses va_list warning
           '-fno-strict-overflow',
         ],
       },
 
+      # ARM64 cross-build
+      'Dart_Linux_xarm64_Base': {
+        'abstract': 1,
+        'target_conditions': [
+        ['_toolset=="target"', {
+          'cflags': [ '-O3', ],
+        }],
+        ['_toolset=="host"', {
+          'cflags': ['-O3', '-m64', '-msse2'],
+          'ldflags': ['-m64'],
+        }]]
+      },
+
+      # ARM64 native build
+      'Dart_Linux_arm64_Base': {
+        'abstract': 1,
+        'cflags': [ '-O3', ],
+      },
+
       'Dart_Linux_simmips_Base': {
         'abstract': 1,
         'cflags': [ '-O3', '-m32', '-msse2' ],
         'ldflags': [ '-m32', ],
       },
 
       # MIPS cross-build
       'Dart_Linux_xmips_Base': {
         'abstract': 1,
         'target_conditions': [
@@ skipping 39 matching lines @@
           # The sampling profiler uses the frame pointer to walk the stack.
           '-fno-omit-frame-pointer',
           # Clang on Linux will still omit frame pointers from leaf functions
           # unless told otherwise:
           # '-mno-omit-leaf-frame-pointer',
         ],
       },
     },
   },
 }