Fix bashism.

Index: configure
--- configure.orig
+++ configure
@@ -22713,7 +22713,7 @@ then
 
     loop=${enable_monitors},
 
-    while echo $loop | grep \, &> /dev/null
+    while echo $loop | grep -q \,
     do
         monitor=${loop%%\,*}
         loop=${loop#*\,}
