Fix progress bar flicker with -L

This was caused by -L calling setLogFormat() again, which caused the
creation of a new progress bar without destroying the old one. So we
had two progress bars clobbering each other.

We should change 'logger' to be a smart pointer, but I'll do that in a
future PR.

Fixes #6931.

src/libmain/loggers.cc

@@ -30,8 +30,11 @@ Logger * makeDefaultLogger() {
         return makeJSONLogger(*makeSimpleLogger(true));
     case LogFormat::bar:
         return makeProgressBar();
-    case LogFormat::barWithLogs:
-        return makeProgressBar(true);
+    case LogFormat::barWithLogs: {
+        auto logger = makeProgressBar();
+        logger->setPrintBuildLogs(true);
+        return logger;
+    }
     default:
         abort();
     }