[ios] Assert that Xcode version is recent enough

The template intent_definition requires intentbuilderc version
shipped with Xcode 11.4 or higher. Add a assertion failing at
`gn gen` time to avoid cryptic error at compilation time.

Bug: 1104769
Change-Id: I89b9a66ce8101138749bebd9f777e1e65ff3373a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2302637
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789521}

build/ios/intent_definition.gni

@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/ios/ios_sdk.gni")
+
 # Template to compile an .intentdefinition file.
 #
 # Arguments
@@ -24,6 +26,9 @@ template("intent_definition") {
   assert(defined(invoker.intent_names) && invoker.intent_names != [],
          "intent_names must be defined for $target_name")
 
+  assert(xcode_version_int >= 1140,
+         "intent_definition requires Xcode 11.4 or higher")
+
   _compile_intent_target = "${target_name}_compile_intent"
   _compile_intent_output =
       "$target_gen_dir/" + get_path_info(invoker.intent_file, "file")