Remove direct use of objc linking provider (#2023)

This was removed on bazel @ HEAD but still required for supporting older
versions.

Fixes #2020

apple/apple_static_library.bzl

@@ -49,16 +49,20 @@ def _apple_static_library_impl(ctx):
         collect_data = True,
     )
 
-    return [
+    providers = [
         DefaultInfo(files = depset(files_to_build), runfiles = runfiles),
         AppleBinaryInfo(
             binary = link_result.library,
             infoplist = None,
         ),
-        link_result.objc,
         link_result.output_groups,
     ]
 
+    if link_result.objc:
+        providers.append(link_result.objc)
+
+    return providers
+
 apple_static_library = rule(
     implementation = _apple_static_library_impl,
     attrs = dicts.add(

apple/internal/linking_support.bzl

@@ -213,7 +213,7 @@ def _register_binary_linking_action(
         binary = fat_binary,
         cc_info = linking_outputs.cc_info,
         debug_outputs_provider = linking_outputs.debug_outputs_provider,
-        objc = linking_outputs.objc,
+        objc = getattr(linking_outputs, "objc", None),
         outputs = linking_outputs.outputs,
         output_groups = linking_outputs.output_groups,
     )
@@ -253,7 +253,7 @@ def _register_static_library_linking_action(ctx):
 
     return struct(
         library = fat_library,
-        objc = linking_outputs.objc,
+        objc = getattr(linking_outputs, "objc", None),
         outputs = linking_outputs.outputs,
         output_groups = linking_outputs.output_groups,
     )