fix more clippy::style findings

match_result_ok
obfuscated_if_else
single_char_add
writeln_empty_string
collapsible_match
iter_cloned_collect
unnecessary_mut_passed

compiler/rustc_monomorphize/src/partitioning/mod.rs

@@ -305,7 +305,7 @@ where
                 );
             }
 
-            let _ = writeln!(s, "");
+            let _ = writeln!(s);
         }
 
         std::mem::take(s)