Use Span::apply_mark where possible

src/libsyntax_ext/concat.rs

@@ -57,6 +57,6 @@ pub fn expand_syntax_ext(cx: &mut base::ExtCtxt,
             }
         }
     }
-    let sp = sp.with_ctxt(sp.ctxt().apply_mark(cx.current_expansion.mark));
+    let sp = sp.apply_mark(cx.current_expansion.mark);
     base::MacEager::expr(cx.expr_str(sp, Symbol::intern(&accumulator)))
 }