Emit 'linking not required' messages only with -v 2 or above.

Similar in philosophy to the 'Skipping' patch, this is another case of
printing noisy messages when no work is being done. This patch makes the
building-when-nothing-to-do case smoother.

compiler/main/DriverPipeline.hs

@@ -302,7 +302,7 @@ link BatchCompile dflags batch_attempt_linking hpt
 			any (t <) (map linkableTime linkables)
 
 	if dopt Opt_RecompChecking dflags && not linking_needed
-	   then do debugTraceMsg dflags 1 (text exe_file <+> ptext SLIT("is up to date, linking not required."))
+	   then do debugTraceMsg dflags 2 (text exe_file <+> ptext SLIT("is up to date, linking not required."))
 		   return Succeeded
 	   else do