Add tinyxml2 to hwasan-postsubmit

Test: Run tests under HWASan.
Bug: 193568145
Change-Id: Ib4f56d9c9061adbdbe49e28dd0a5db76b1f32968

TEST_MAPPING

@@ -3,5 +3,10 @@
     {
       "name": "tinyxml2-tests"
     }
+  ],
+  "hwasan-postsubmit": [
+    {
+      "name": "tinyxml2-tests"
+    }
   ]
 }