Use autoconf to check for features needed by Networking TS
* config.h.in: Regenerate.
* configure: Regenerate.
* configure.ac: Check for headers used by Networking TS.
* include/experimental/executor: Include <condition_variable>
instead of <mutex>.
* include/experimental/internet: Use autoconf macros for available
headers. Include <sys/socket.h> for. Remove <cstring> and use
__builtin_memcpy and __builtin_strchr.
(resolver_errc) [!_GLIBCXX_HAVE_NETDB_H]: Do not define.
(address_v4::to_string, address_v6::to_string)
[!_GLIBCXX_HAVE_ARPA_INET_H]: Likewise.
(basic_resolver_results) [!_GLIBCXX_HAVE_NETDB_H]: Make private
constructors report errors.
[!_GLIBCXX_HAVE_NETINET_TCP_H] (tcp::no_delay): Do not define.
* include/experimental/io_context: Likewise.
* include/experimental/socket: Likewise.
[!_GLIBCXX_HAVE_SYS_SOCKET_H, !_GLIBCXX_HAVE_POLL_H] (socket_base): Do
not define nested types when relevant header not available.
(__socket_impl::native_non_blocking) [!_GLIBCXX_HAVE_FCNTL_H]: Report
an error.
(__basic_socket_impl::open, __basic_socket_impl::local_endpoint)
(__basic_socket_impl::bind) [!_GLIBCXX_HAVE_SYS_SOCKET_H]: Likewise.
(__basic_socket_impl::io_control) [!_GLIBCXX_HAVE_SYS_IOCTL_H]:
Likewise.
(basic_socket::at_mark, basic_socket::shutdown)
(basic_socket::remote_endpoint, basic_socket::connect)
(basic_socket::async_connect) [!_GLIBCXX_HAVE_SYS_SOCKET_H]: Likewise.
(basic_socket::available) [_GLIBCXX_HAVE_SYS_IOCTL_H]: Check macro
for <sys/ioctl.h> availability.
(basic_socket::wait) [!_GLIBCXX_HAVE_POLL_H]: Likewise.
(basic_datagram_socket::receive, basic_datagram_socket::async_receive)
(basic_datagram_socket::receive_from)
(basic_datagram_socket::async_receive_from)
(basic_datagram_socket::send, basic_datagram_socket::async_send)
(basic_datagram_socket::send_to, basic_datagram_socket::async_send_to)
[!_GLIBCXX_HAVE_SYS_SOCKET_H]: Likewise.
(basic_stream_socket::receive, basic_stream_socket::async_receive)
(basic_stream_socket::send, basic_stream_socket::async_send)
[!_GLIBCXX_HAVE_SYS_SOCKET_H]: Likewise.
(basic_socket_acceptor::listen, basic_socket_acceptor::accept)
(basic_socket_acceptor::async_accept) [!_GLIBCXX_HAVE_SYS_SOCKET_H]:
Likewise.
(basic_socket_acceptor::wait) [!_GLIBCXX_HAVE_POLL_H]: Likewise.
From-SVN: r265203
82a0f2fd10