Add some tests to gcstress knownfailures

Several tests were broken under gcstress by the new libbacktrace based
gcstress.

The tests are:
  * 151-OpenFileLimit, the new gcstress needs to be able to open
    /proc/self/maps to function.
  * 530-checker-lse2, The test times out due to the 30% slowdown.
  * 712-varhandle-invocations & 624-checker-stringops, The new
    gcstress with its more accurate thread walking seems to expose
    gc-bugs through these tests. See b/111545159.

Bug: 111544552
Bug: 111543628
Bug: 111545159
Test: ./test/testrunner/testrunner.py --host --gcstress
Change-Id: I08d93e2c794c2b91aa5c0ed1c503846f17657231
diff --git a/test/knownfailures.json b/test/knownfailures.json
index 2b7a9b0..3033079 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -1010,6 +1010,24 @@
         "description": ["Test throws exception before or during OOME."]
     },
     {
+        "tests": ["151-OpenFileLimit"],
+        "variant": "gcstress",
+        "bug": "b/111544552",
+        "description" : ["Gcstress requires the ability to open at least one file which means this test fails when it runs out."]
+    },
+    {
+        "tests": ["530-checker-lse2"],
+        "variant": "gcstress",
+        "bug": "b/111543628",
+        "description" : ["Test seems to timeout when run with gcstress due to slower unwinding by libbacktrace"]
+    },
+    {
+        "tests": ["712-varhandle-invocations", "624-checker-stringops"],
+        "variant": "optimizing & gcstress | speed-profile & gcstress",
+        "bug": "b/111545159",
+        "description": ["These tests seem to expose some error with our gc when run in these configurations"]
+    },
+    {
         "tests": ["021-string2"],
         "variant": "jit & debuggable",
         "bug": "b/109791792",