Revert "Remove cmake-config support of HarfBuzz"

This reverts commit 75efa893433b6f352c28bda9d0a92683244900aa.
diff --git a/configure.ac b/configure.ac
index 7c0d857..1f94273 100644
--- a/configure.ac
+++ b/configure.ac
@@ -478,6 +478,7 @@
 AC_CONFIG_FILES([
 Makefile
 src/Makefile
+src/harfbuzz-config.cmake
 util/Makefile
 test/Makefile
 test/api/Makefile