Rollup merge of #39961 - redox-os:redox, r=alexcrichton

Fix compilation on Redox

This updates the Redox sys module to fix compilation.

The functions peek and peek_from are added to TcpStream and UdpSocket as stubs. The sys::backtrace module is now included correctly

src/libstd/sys/redox/mod.rs

@@ -13,7 +13,7 @@
 use io::{self, ErrorKind};
 
 pub mod args;
-#[cfg(any(not(cargobuild), feature = "backtrace"))]
+#[cfg(feature = "backtrace")]
 pub mod backtrace;
 pub mod condvar;
 pub mod env;

src/libstd/sys/redox/net/tcp.rs

@@ -63,6 +63,10 @@ impl TcpStream {
         Ok(path_to_local_addr(path.to_str().unwrap_or("")))
     }
 
+    pub fn peek(&self, _buf: &mut [u8]) -> Result<usize> {
+        Err(Error::new(ErrorKind::Other, "TcpStream::peek not implemented"))
+    }
+
     pub fn shutdown(&self, _how: Shutdown) -> Result<()> {
         Err(Error::new(ErrorKind::Other, "TcpStream::shutdown not implemented"))
     }

src/libstd/sys/redox/net/udp.rs

@@ -87,6 +87,14 @@ impl UdpSocket {
         Ok(path_to_local_addr(path.to_str().unwrap_or("")))
     }
 
+    pub fn peek(&self, _buf: &mut [u8]) -> Result<usize> {
+        Err(Error::new(ErrorKind::Other, "UdpSocket::peek not implemented"))
+    }
+
+    pub fn peek_from(&self, _buf: &mut [u8]) -> Result<(usize, SocketAddr)> {
+        Err(Error::new(ErrorKind::Other, "UdpSocket::peek_from not implemented"))
+    }
+
     pub fn broadcast(&self) -> Result<bool> {
         Err(Error::new(ErrorKind::Other, "UdpSocket::broadcast not implemented"))
     }