fix check on setting of R__KRB5 flag.

git-svn-id: http://root.cern.ch/svn/root/trunk@7180 27541ba8-7e3a-0410-8455-c3a389f83636

configure

@@ -1651,7 +1651,7 @@ if test ! "x$enable_krb5" = "xno" ; then
         enable_krb5="no"
     fi
 
-    if test ! "x$enable_krb5" = "x" ; then
+    if test ! "x$enable_krb5" = "xno" ; then
         krb5extracflags="-DR__KRB5"
     fi
 fi