rustdoc: Stabilize --diagnostic-width

src/librustdoc/lib.rs

@@ -461,7 +461,7 @@ fn opts() -> Vec<RustcOptGroup> {
                 "human|json|short",
             )
         }),
-        unstable("diagnostic-width", |o| {
+        stable("diagnostic-width", |o| {
             o.optopt(
                 "",
                 "diagnostic-width",

src/test/rustdoc-ui/diagnostic-width.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Zunstable-options --diagnostic-width=10
+// compile-flags: --diagnostic-width=10
 #![deny(rustdoc::bare_urls)]
 
 /// This is a long line that contains a http://link.com