fix SyntheticTestUtils

Change-Id: I757e49ea9f0efbf60479c258ce8a93e0a1df1a11
diff --git a/src/test/java/com/android/tools/r8/synthesis/SyntheticItemsTestUtils.java b/src/test/java/com/android/tools/r8/synthesis/SyntheticItemsTestUtils.java
index 8cc71c8..804c5f8 100644
--- a/src/test/java/com/android/tools/r8/synthesis/SyntheticItemsTestUtils.java
+++ b/src/test/java/com/android/tools/r8/synthesis/SyntheticItemsTestUtils.java
@@ -76,7 +76,8 @@
   public static boolean isExternalSynthetic(ClassReference reference) {
     for (SyntheticKind kind : SyntheticKind.values()) {
       if (kind == SyntheticKind.RECORD_TAG
-          || kind == SyntheticKind.EMULATED_INTERFACE_MARKER_CLASS) {
+          || kind == SyntheticKind.EMULATED_INTERFACE_MARKER_CLASS
+          || kind == SyntheticKind.RETARGET_STUB) {
         continue;
       }
       if (kind.isFixedSuffixSynthetic) {