Properly compile multidex for tests when using Jack.

Bug: 19687200
Change-Id: I8c5771ccd474aa06001c3a48cc82550589ac7055
diff --git a/test/MultiDex/main.jpp b/test/MultiDex/main.jpp
new file mode 100644
index 0000000..a5d7a6c
--- /dev/null
+++ b/test/MultiDex/main.jpp
@@ -0,0 +1,3 @@
+main:
+  @@com.android.jack.annotations.ForceInMainDex
+  class Main