Change `SIGPIPE` ui from `#[unix_sigpipe = "..."]` to `-Zon-broken-pipe=...`

In the stabilization attempt of `#[unix_sigpipe = "sig_dfl"]`, a concern
was raised related to using a language attribute for the feature: Long
term, we want `fn lang_start()` to be definable by any crate, not just
libstd. Having a special language attribute in that case becomes
awkward.

So as a first step towards towards the next stabilization attempt, this
PR changes the `#[unix_sigpipe = "..."]` attribute to a compiler flag
`-Zon-broken-pipe=...` to remove that concern, since now the language
is not "contaminated" by this feature.

Another point was also raised, namely that the ui should not leak
**how** it does things, but rather what the **end effect** is. The new
flag uses the proposed naming. This is of course something that can be
iterated on further before stabilization.

1 files changed, 1 insertions, 3 deletions

diff --git a/tests/ui/process/println-with-broken-pipe.rs b/tests/ui/process/println-with-broken-pipe.rs
index 1df8c765cbd..798db3c0f8c 100644
--- a/tests/ui/process/println-with-broken-pipe.rs
+++ b/tests/ui/process/println-with-broken-pipe.rs
@@ -6,16 +6,14 @@
 //@ ignore-horizon
 //@ ignore-android
 //@ normalize-stderr-test ".rs:\d+:\d+" -> ".rs:LL:CC"
+//@ compile-flags: -Zon-broken-pipe=error
 
 // Test what the error message looks like when `println!()` panics because of
 // `std::io::ErrorKind::BrokenPipe`
 
-#![feature(unix_sigpipe)]
-
 use std::env;
 use std::process::{Command, Stdio};
 
-#[unix_sigpipe = "sig_ign"]
 fn main() {
     let mut args = env::args();
     let me = args.next().unwrap();