Auto merge of #4713 - alexcrichton:fix-bsd, r=matklad

Fix compilation on more platforms

Author: bors

src/cargo/core/shell.rs

@@ -287,7 +287,7 @@ impl ColorChoice {
     }
 }
 
-#[cfg(unix)]
+#[cfg(any(target_os = "linux", target_os = "macos"))]
 mod imp {
     use std::mem;
 
@@ -308,6 +308,13 @@ mod imp {
     }
 }
 
+#[cfg(all(unix, not(any(target_os = "linux", target_os = "macos"))))]
+mod imp {
+    pub fn stderr_width() -> Option<usize> {
+        None
+    }
+}
+
 #[cfg(windows)]
 mod imp {
     use std::mem;