Rollup merge of #123476 - devnexen:std_net_solaris_exclbind, r=Mark-Simulacrum

std::net: adding `unix_socket_exclbind` feature for solaris/illumos.

allows to have a tigher control over the binding exclusivness of the socket.

ACP: rust-lang/libs-team#366

Author: matthiaskrgr