Hide private functions from createrepo_c library

[ppisar]

The library exported 274 symbols. However, many of them were not declared in any public header file, hence application were not supposed to use them. In other words, the library offered functions which were not part of an API. That was not good because:

These private functions enlarged an attack surface. These private functions polluted binary interface and triggered warnigs by ABI checkers (e.g. when libXML-2.12.0 changed xmlParserCtxt structure). These private functions could fool a user into calling them and that would increase a pressure on broadening createrepo_c API.

I reviewed all the 274 symbols and hid 52 of them:

cr_char_handler cr_cktype_from_zck cr_db_add_filelists_pkg cr_db_add_other_pkg cr_db_add_primary_pkg cr_db_destroy_filelists_statements cr_db_destroy_other_statements cr_db_destroy_primary_statements cr_db_prepare_filelists_statements cr_db_prepare_other_statements cr_db_prepare_primary_statements cr_destroy_metadata_hashtable cr_free_values cr_get_compressed_content_stat cr_new_metadata_hashtable cr_newpkgcb cr_package_copy_into cr_prestodeltatask_free cr_remove_dir_cb cr_xml_dump_delta cr_xml_dump_filelists_chunk cr_xml_dump_filelists_items cr_xml_dump_files cr_xml_dump_int cr_xml_dump_other_changelog cr_xml_dump_other_items cr_xml_dump_repomd_body cr_xml_dump_repomd_record cr_xml_dump_updatecollectionmodule cr_xml_dump_updatecollectionpackages cr_xml_dump_updateinfo_body cr_xml_dump_updateinforecord_internal cr_xml_dump_updateinforecord_pkglist cr_xml_dump_updateinforecord_references cr_xmlfile_write_xml_footer cr_xmlfile_write_xml_header cr_xmlNewProp cr_xmlNewTextChild cr_xml_parse_filelists_internal cr_xml_parse_other_internal cr_xml_parse_primary_internal cr_xml_parser_data cr_xml_parser_data_free cr_xml_parser_generic cr_xml_parser_generic_from_string cr_xml_parser_strtoll cr_xml_parser_warning filelists_parser_data_new other_parser_data_new prepare_split_media_baseurl primary_parser_data_new unescape_ampersand_from_values

I kept these 10 private symbols because they are called either from createrepo_c program or from a Python binding:

cr_compress_groupfile cr_delayed_dump_run cr_delayed_dump_set cr_distrotag_new cr_dumper_thread cr_metadata_load_modulemd cr_metadata_modulemd cr_repomd_compare cr_xml_dump_primary_base_items cr_xml_dump_primary_dump_pco

This patch minimizes a symbol table by making the private functions static or by setting their visibility to a hidden state. As result, they disappear from the library binary interface.

[ppisar]

Oh my god. "make test" and "make tests" differ.