Add only-unix to sigpipe tests

Author: saethlin

tests/ui/runtime/on-broken-pipe/error.rs

@@ -1,6 +1,7 @@
 //@ run-pass
 //@ aux-build:sigpipe-utils.rs
 //@ compile-flags: -Zon-broken-pipe=error
+//@ only-unix because SIGPIPE is a unix thing
 
 fn main() {
     extern crate sigpipe_utils;

tests/ui/runtime/on-broken-pipe/inherit.rs

@@ -4,6 +4,7 @@
 //@ aux-bin: assert-inherit-sig_ign.rs
 //@ run-pass
 //@ compile-flags: -Zon-broken-pipe=kill
+//@ only-unix because SIGPIPE is a unix thing
 
 #![feature(rustc_private)]
 

tests/ui/runtime/on-broken-pipe/kill.rs

@@ -1,6 +1,7 @@
 //@ run-pass
 //@ aux-build:sigpipe-utils.rs
 //@ compile-flags: -Zon-broken-pipe=kill
+//@ only-unix because SIGPIPE is a unix thing
 
 fn main() {
     extern crate sigpipe_utils;

tests/ui/runtime/on-broken-pipe/not-used.rs

@@ -1,5 +1,6 @@
 //@ run-pass
 //@ aux-build:sigpipe-utils.rs
+//@ only-unix because SIGPIPE is a unix thing
 
 fn main() {
     extern crate sigpipe_utils;

tests/ui/runtime/on-broken-pipe/with-rustc_main.rs

@@ -1,6 +1,7 @@
 //@ run-pass
 //@ aux-build:sigpipe-utils.rs
 //@ compile-flags: -Zon-broken-pipe=kill
+//@ only-unix because SIGPIPE is a unix thing
 
 #![feature(rustc_attrs)]