ART: Disable two tests for ASAN/interp-ac.

These are flaky because the stack guard reservation is
insufficient for this configuration.

Test: SANITIZE_HOST=address testrunner.py --host --interp-ac \
      -t 018-stack-overflow -t 107-int-math2  # All skipped.
Test: SANITIZE_TARGET=address testrunner.py --target --interp-ac \
      -t 018-stack-overflow -t 107-int-math2  # All skipped.
Bug: 31098551
Change-Id: I2029e0424c3717efa599c3b2e637f888646ead31
diff --git a/test/knownfailures.json b/test/knownfailures.json
index 0a179c7..6004f25 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -578,6 +578,30 @@
     },
     {
         "tests": [
+            "018-stack-overflow",
+            "107-int-math2"
+        ],
+        "description": [
+            "Insufficient stack guards for ASAN."
+        ],
+        "variant": "interp-ac & host",
+        "env_vars": {"SANITIZE_HOST": "address"},
+        "bug": "b/31098551"
+    },
+    {
+        "tests": [
+            "018-stack-overflow",
+            "107-int-math2"
+        ],
+        "description": [
+            "Insufficient stack guards for ASAN."
+        ],
+        "variant": "interp-ac & target",
+        "env_vars": {"SANITIZE_TARGET": "address"},
+        "bug": "b/31098551"
+    },
+    {
+        "tests": [
             "059-finalizer-throw",
             "074-gc-thrash",
             "911-get-stack-trace",