Experimental feature to do header thinning of Objective-C compilation actions.

--
PiperOrigin-RevId: 146385106
MOS_MIGRATED_REVID=146385106
diff --git a/tools/objc/BUILD b/tools/objc/BUILD
index ae32daf..f1852f4 100644
--- a/tools/objc/BUILD
+++ b/tools/objc/BUILD
@@ -159,3 +159,9 @@
     name = "protobuf_well_known_types",
     srcs = ["dummy.proto"],
 )
+
+# Intentionally empty
+filegroup(
+    name = "header_scanner",
+    srcs = [],
+)