7102300: performance warnings cause results diff failure in Test6890943

Summary: Strip lines matching the performance warning from the output before diff.
Reviewed-by: kvn

test/compiler/5091921/Test6890943.sh

 #!/bin/sh
 # 
-# Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2011, 2013, Oracle and/or its affiliates. All rights reserved.
 # DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 # 
 # This code is free software; you can redistribute it and/or modify it
@@ -52,7 +52,10 @@ cp ${TESTSRC}/Test6890943.sh .
 
 ${TESTJAVA}/bin/javac -d . Test6890943.java
 
-${TESTJAVA}/bin/java -XX:-PrintVMOptions ${TESTVMOPTS} Test6890943 < input6890943.txt > test.out 2>&1
+${TESTJAVA}/bin/java -XX:-PrintVMOptions -XX:+IgnoreUnrecognizedVMOptions ${TESTVMOPTS} Test6890943 < input6890943.txt > pretest.out 2>&1
+
+# This test sometimes tickles an unrelated performance warning that interferes with diff.
+grep -v 'warning: Performance bug: SystemDictionary' pretest.out > test.out
 
 diff output6890943.txt test.out