Disable 1339-dead-reference-safe when debuggable

We keep dead references around in debuggable builds, and the test
doesn't tolerate that.

Test: art/test/testrunner/testrunner.py -j70 --host --64 --debuggable
Change-Id: I1f2d7ad87a337d1f13ee80fd16892280cfe987b9
diff --git a/test/knownfailures.json b/test/knownfailures.json
index c4764e8..e32d23d 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -1173,6 +1173,11 @@
         "description": ["Tests are expected to fail with baseline."]
     },
     {
+        "tests": ["1339-dead-reference-safe"],
+        "variant": "debuggable",
+        "description": [ "Fails to eliminate dead reference when debuggable." ]
+    },
+    {
         "tests": ["708-jit-cache-churn"],
         "variant": "jit-on-first-use",
         "bug": "b/120112467",