Use xcrun to discover Apple SDK paths (#912)

Tested in https://github.com/flutter/engine/pull/55818

build/config/ios/ios_sdk.py

diff --git a/build/config/ios/ios_sdk.py b/build/config/ios/ios_sdk.py
index 607a425..bcbd700 100644
--- a/build/config/ios/ios_sdk.py
+++ b/build/config/ios/ios_sdk.py
@@ -93,11 +93,10 @@
 
   for sdk in sdks:
     command =  [
-      'xcodebuild',
-      '-version',
-      '-sdk',
+      'xcrun',
+      '--sdk',
       sdk,
-      'Path'
+      '--show-sdk-path',
     ]
     sdk_output = run_command_with_retry(command, timeout=300)
     if symlink_path:

build/mac/find_sdk.py

diff --git a/build/mac/find_sdk.py b/build/mac/find_sdk.py
index 73cf268..2471eba 100755
--- a/build/mac/find_sdk.py
+++ b/build/mac/find_sdk.py
@@ -91,32 +91,14 @@
       '|sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer| '
       'if you are using Xcode 4.') % job.returncode)
 
-  sdk_command = ['xcodebuild',
-    '-showsdks',
-    '-json']
-  sdk_json_output = run_command_with_retry(sdk_command, timeout=300)
-  sdk_json = json.loads(sdk_json_output)
-
-  best_sdk = None
-  sdk_output = None
-
-  # Xcode can return the same version for different symlinked paths.
-  # Sort by path to keep the list stable between runs.
-  for properties in sorted(list(sdk_json), key=lambda d: d['sdkPath']):
-    # Filter out macOS DriverKit, watchOS, AppleTV, and other SDKs.
-    if properties.get('platform') != 'macosx' or 'driver' in properties.get('canonicalName'):
-      continue
-    sdk_version = properties['sdkVersion']
-    parsed_version = parse_version(sdk_version)
-    if (parsed_version >= parse_version(min_sdk_version) and
-          (not best_sdk or parsed_version < parse_version(best_sdk))):
-      best_sdk = sdk_version
-      sdk_output = properties['sdkPath']
-
-  if not best_sdk:
-    print(sdk_json_output)
-    raise Exception('No %s+ SDK found' % min_sdk_version)
-
+  # xcrun --sdk macosx  --show-sdk-path
+  sdk_command = [
+    'xcrun',
+    '--sdk',
+    'macosx',
+    '--show-sdk-path',
+  ]
+  sdk_output = run_command_with_retry(sdk_command, timeout=300)
   if symlink_path:
     sdks_path = os.path.join(symlink_path, 'SDKs')
     symlink_target = os.path.join(sdks_path, os.path.basename(sdk_output))
@@ -125,7 +107,6 @@
 
   if not options.as_gclient_hook:
     print(sdk_output)
-    print(best_sdk)
   return 0