[android][build-script] Update the default arch to AArch64, as that is by far the most commonly used now

Author: finagolfin

utils/build_swift/build_swift/driver_arguments.py

@@ -1403,7 +1403,7 @@ def create_argument_parser():
 
     option('--android-arch', store,
            choices=['armv7', 'aarch64', 'x86_64'],
-           default='armv7',
+           default='aarch64',
            help='The target architecture when building for Android. '
                 'Currently, only armv7, aarch64, and x86_64 are supported. '
                 '%(default)s is the default.')

utils/build_swift/tests/expected_options.py

@@ -41,7 +41,7 @@
     'android_api_level': '21',
     'android_deploy_device_path': '/data/local/tmp',
     'android_ndk': None,
-    'android_arch': 'armv7',
+    'android_arch': 'aarch64',
     'assertions': True,
     'benchmark': False,
     'benchmark_num_o_iterations': 3,
@@ -768,7 +768,7 @@ class BuildScriptImplOption(_BaseOption):
     ChoicesOption('--swift-analyze-code-coverage',
                   choices=['false', 'not-merged', 'merged']),
     ChoicesOption('--android-arch',
-                  choices=['armv7', 'aarch64']),
+                  choices=['armv7', 'aarch64', 'x86_64']),
 
     StrOption('--android-api-level'),
     StrOption('--build-args'),