Add another test to the list of known failures for gcstress/debug.

Test: run-libcore-tests
Change-Id: Ic77111f6501e12891c24a2f0f79107e0745f3500
diff --git a/tools/libcore_gcstress_debug_failures.txt b/tools/libcore_gcstress_debug_failures.txt
index 0d8cebc..a42f479 100644
--- a/tools/libcore_gcstress_debug_failures.txt
+++ b/tools/libcore_gcstress_debug_failures.txt
@@ -40,6 +40,7 @@
           "jsr166.StampedLockTest#testReadLockInterruptibly",
           "jsr166.StampedLockTest#testWriteLockInterruptibly",
           "jsr166.TimeUnitTest#testConvert",
+          "jsr166.TreeSetTest#testRecursiveSubSets",
           "libcore.java.lang.OldThreadTest#test_getState",
           "libcore.java.lang.StringTest#testFastPathString_wellFormedUtf8Sequence",
           "libcore.java.math.BigIntegerTest#test_Constructor_IILjava_util_Random",