Change a #[cfg()] to a cfg!()

src/librustc_driver/driver.rs

@@ -246,8 +246,7 @@ macro_rules! controller_entry_point {
         })??
     };
 
-    #[cfg(not(feature="llvm"))]
-    {
+    if cfg!(not(feature="llvm")) {
         let (_, _) = (outputs, trans);
         sess.fatal("LLVM is not supported by this rustc");
     }