Add library retargeting classes into retarget package

This will ensure that we keep the j$ prefix for the classes.

Change-Id: I944e5e43083713c0fb0d443dd3938dd1ecc58b76

src/main/java/com/android/tools/r8/ir/desugar/DesugaredLibraryRetargeter.java

diff --git a/src/main/java/com/android/tools/r8/ir/desugar/DesugaredLibraryRetargeter.java b/src/main/java/com/android/tools/r8/ir/desugar/DesugaredLibraryRetargeter.java
index 3dc74ac..5b505fa 100644
--- a/src/main/java/com/android/tools/r8/ir/desugar/DesugaredLibraryRetargeter.java
+++ b/src/main/java/com/android/tools/r8/ir/desugar/DesugaredLibraryRetargeter.java
@@ -64,6 +64,7 @@
 
 public class DesugaredLibraryRetargeter {
 
+  public static final String RETARGET_PACKAGE = "retarget/";
   public static final String DESUGAR_LIB_RETARGET_CLASS_NAME_PREFIX =
       "$r8$retargetLibraryMember$virtualDispatch";
 
@@ -675,6 +676,7 @@
                 .options()
                 .desugaredLibraryConfiguration
                 .getSynthesizedLibraryClassesPackagePrefix()
+            + RETARGET_PACKAGE
             + DESUGAR_LIB_RETARGET_CLASS_NAME_PREFIX
             + '$'
             + method.getHolderType().getName()