native: Ignore SIGPIPE by default

Some unix platforms will send a SIGPIPE signal instead of returning EPIPE from a
syscall by default. The native runtime doesn't install a SIGPIPE handler,
causing the program to die immediately in this case. This brings the behavior in
line with libgreen by ignoring SIGPIPE and propagating EPIPE upwards to the
application in the form of an IoError.

Closes #13123
auto merge of #13158 : alexcrichton/rust/issue-13123, r=brson

Some unix platforms will send a SIGPIPE signal instead of returning EPIPE from a
syscall by default. The native runtime doesn't install a SIGPIPE handler,
causing the program to die immediately in this case. This brings the behavior in
line with libgreen by ignoring SIGPIPE and propagating EPIPE upwards to the
application in the form of an IoError.

Closes #13123