-# Make sure the generated headers are up-to-date. This must be kept in
-# sync with the AC_CONFIG_HEADER invocations in autoconf/configure.ac
+# Make sure the generated files are up-to-date. This must be kept in
+# sync with the AC_CONFIG_HEADER and AC_CONFIG_FILE invocations in
+# autoconf/configure.ac.
+# Note that Makefile.config is covered by its own separate rule
+# in Makefile.rules where it can be reused by sub-projects.