Begins work on ARM64, first assembler test.

tools/gyp/configurations.gypi

Index: tools/gyp/configurations.gypi
===================================================================
--- tools/gyp/configurations.gypi	(revision 34648)
+++ tools/gyp/configurations.gypi	(working copy)
@@ -18,6 +18,7 @@
       ['"<(target_arch)"=="x64"', { 'dart_target_arch': 'X64', }],
       ['"<(target_arch)"=="arm"', { 'dart_target_arch': 'ARM', }],
       ['"<(target_arch)"=="simarm"', { 'dart_target_arch': 'SIMARM', }],
+      ['"<(target_arch)"=="simarm64"', { 'dart_target_arch': 'SIMARM64', }],
       ['"<(target_arch)"=="mips"', { 'dart_target_arch': 'MIPS', }],
       ['"<(target_arch)"=="simmips"', { 'dart_target_arch': 'SIMMIPS', }],
       [ 'OS=="linux"', { 'dart_target_os': 'Linux', } ],
@@ -59,6 +60,13 @@
         ]
       },
 
+      'Dart_simarm64_Base': {
+        'abstract': 1,
+        'defines': [
+          'TARGET_ARCH_ARM64',
+        ]
+      },
+
       'Dart_arm_Base': {
         'abstract': 1,
         'defines': [
@@ -150,6 +158,27 @@
         ],
       },
 
+      'DebugSIMARM64': {
+        'inherit_from': [
+          'Dart_Base', 'Dart_simarm64_Base', 'Dart_Debug',
+          'Dart_<(dart_target_os)_Base',
+          'Dart_<(dart_target_os)_simarm64_Base',
+          'Dart_<(dart_target_os)_Debug',
+        ],
+        'defines': [
+          'DEBUG',
+        ],
+      },
+
+      'ReleaseSIMARM64': {
+        'inherit_from': [
+          'Dart_Base', 'Dart_simarm64_Base', 'Dart_Release',
+          'Dart_<(dart_target_os)_Base',
+          'Dart_<(dart_target_os)_simarm64_Base',
+          'Dart_<(dart_target_os)_Release',
+        ],
+      },
+
       'DebugSIMMIPS': {
         'inherit_from': [
           'Dart_Base', 'Dart_simmips_Base', 'Dart_Debug',