[illumos/solaris] set MSG_NOSIGNAL while writing to sockets
Both these platforms have MSG_NOSIGNAL available, and we should set it for socket writes in the event that the SIGPIPE handler has been reset to SIG_DFL (i.e. terminate the process).
I've verified via a quick program at
https://github.com/sunshowers/msg-nosignal-test/ that even when the SIGPIPE handler is reset to SIG_DFL, writes to closed TCP sockets now error out with EPIPE. (Under ordinary circumstances UDP writes won't cause MSG_NOSIGNAL.)
However, I couldn't find any existing tests which verified the MSG_NOSIGNAL behavior.
2b58d8c08c