Fix --tool=D8|R8 selection for JCTF

Bug:
Change-Id: I4277d8b24e4bd3e8c4c17daadd8b3da3ad0ba9a9
diff --git a/build.gradle b/build.gradle
index 6667647..32806ba 100644
--- a/build.gradle
+++ b/build.gradle
@@ -684,9 +684,11 @@
     if (project.hasProperty('tool')) {
         if (project.property('tool') == 'r8') {
             exclude "com/android/tools/r8/art/*/d8/**"
+            exclude "com/android/tools/r8/jctf/d8/**"
         } else {
             assert(project.property('tool') == 'd8')
             exclude "com/android/tools/r8/art/*/r8/**"
+            exclude "com/android/tools/r8/jctf/r8/**"
         }
     }
     if (!project.hasProperty('all_tests')) {