use unused attribute for the parm

From-SVN: r49403

gcc/testsuite/g++.dg/ext/attrib3.C

 // Test that attributes work in a variety of situations.
+// { dg-options -Wunused }
 // { dg-do run }
 
 #define attrib __attribute ((mode (QI)))
+#define attrib2 __attribute ((unused))
 
 attrib signed int a;		// attributes before type are broken
-attrib unsigned int b;
+static attrib unsigned int b;
 
-int foo(attrib int o)		// attribute arguments are broken
+int foo(attrib2 int o)		// attribute arguments are broken
 {
   return (sizeof (a) != 1
 	  || sizeof (b) != 1
-	  || sizeof (o) != 1
 	  || sizeof ((attrib signed int) b) != 1);
 }