Avoid showing the message if we won't show it :)

Makefile.am

@@ -129,7 +129,7 @@ DISTCLEANFILES = STARPU-REVISION
 
 if STARPU_DEVEL
 all-local:
-	if grep -r sys/time.h $$( find $(srcdir)/src $(srcdir)/mpi/src $(srcdir)/include -name \*.[ch] -a \! -name starpu_util.h ) ; \
+	@if grep -r sys/time.h $$( find $(srcdir)/src $(srcdir)/mpi/src $(srcdir)/include -name \*.[ch] -a \! -name starpu_util.h ) ; \
 	then \
 		echo "Please do not include sys/time, it is not available on Windows, include starpu_util.h and use starpu_timing_now() instead" ; \
 		false ; \