Disable 137-cfi and 629-vdex-speed in no-prebuild mode

The tests require speed compile which is no longer the default for no-
prebuild condigs.

Test: testrunner.py --no-prebuild
Bug: 38442248
Change-Id: I75f870e240a9581cfcc0a9a8b42edb885db6d14e
diff --git a/test/knownfailures.json b/test/knownfailures.json
index f6260bb..dee3b8d 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -711,5 +711,11 @@
         "tests": "655-jit-clinit",
         "description": [ "Currently broken in debug mode"],
         "variant": "debug"
+    },
+    {
+        "tests": ["137-cfi", "629-vdex-speed"],
+        "description": [ "Tests require speed compilation which is no longer the default for",
+                          "no-prebuild configs."],
+        "variant": "no-prebuild"
     }
 ]