fts: Add static library to package files

This explicitly adds libfts.a to the package files and fixes an error
openharmony-standard do_package() that depends on libfts.

Signed-off-by: Thierry Escande <thierry.escande@huawei.com>

recipes-core/fts/fts_%.bbappend

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+FILES:${PN} += "${libdir}/*.a"