/usr/include/apache2/ is in libapache2-mod-perl2-dev 2.0.10-2ubuntu3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/apache2/mod_perl.h
/usr/include/apache2/modperl_apache_compat.h
/usr/include/apache2/modperl_apache_includes.h
/usr/include/apache2/modperl_apr_compat.h
/usr/include/apache2/modperl_apr_includes.h
/usr/include/apache2/modperl_apr_perlio.h
/usr/include/apache2/modperl_bucket.h
/usr/include/apache2/modperl_callback.h
/usr/include/apache2/modperl_cgi.h
/usr/include/apache2/modperl_cmd.h
/usr/include/apache2/modperl_common_debug.h
/usr/include/apache2/modperl_common_includes.h
/usr/include/apache2/modperl_common_log.h
/usr/include/apache2/modperl_common_types.h
/usr/include/apache2/modperl_common_util.h
/usr/include/apache2/modperl_config.h
/usr/include/apache2/modperl_const.h
/usr/include/apache2/modperl_constants.h
/usr/include/apache2/modperl_debug.h
/usr/include/apache2/modperl_directives.h
/usr/include/apache2/modperl_env.h
/usr/include/apache2/modperl_error.h
/usr/include/apache2/modperl_filter.h
/usr/include/apache2/modperl_flags.h
/usr/include/apache2/modperl_global.h
/usr/include/apache2/modperl_gtop.h
/usr/include/apache2/modperl_handler.h
/usr/include/apache2/modperl_hooks.h
/usr/include/apache2/modperl_interp.h
/usr/include/apache2/modperl_io.h
/usr/include/apache2/modperl_io_apache.h
/usr/include/apache2/modperl_largefiles.h
/usr/include/apache2/modperl_log.h
/usr/include/apache2/modperl_mgv.h
/usr/include/apache2/modperl_module.h
/usr/include/apache2/modperl_options.h
/usr/include/apache2/modperl_pcw.h
/usr/include/apache2/modperl_perl.h
/usr/include/apache2/modperl_perl_global.h
/usr/include/apache2/modperl_perl_includes.h
/usr/include/apache2/modperl_perl_pp.h
/usr/include/apache2/modperl_perl_unembed.h
/usr/include/apache2/modperl_svptr_table.h
/usr/include/apache2/modperl_sys.h
/usr/include/apache2/modperl_time.h
/usr/include/apache2/modperl_tipool.h
/usr/include/apache2/modperl_trace.h
/usr/include/apache2/modperl_types.h
/usr/include/apache2/modperl_util.h
/usr/include/apache2/modperl_xs_sv_convert.h
/usr/include/apache2/modperl_xs_typedefs.h
/usr/include/apache2/modperl_xs_util.h