rustc/driver: remove explicit return, add explicit None

Author: ljedrz

src/librustc_driver/driver.rs

@@ -1548,7 +1548,7 @@ pub fn collect_crate_types(session: &Session, attrs: &[ast::Attribute]) -> Vec<c
                         }
                         None
                     }
-                    _ => {
+                    None => {
                         session
                             .struct_span_err(a.span, "`crate_type` requires a value")
                             .note("for example: `#![crate_type=\"lib\"]`")

src/librustc_driver/lib.rs

@@ -997,7 +997,7 @@ impl RustcDefaultCalls {
             return Compilation::Stop;
         }
 
-        return Compilation::Continue;
+        Compilation::Continue
     }