Enable dexpreopt and dex stripping in soong jars

Dexpreopt jars from soong, which also strips classes.dex from
javalib.jar.

Test: m -j checkbuild
Test: unzip -l $OUT/system/framework/core-oj.jar
Change-Id: I06b8efa8993f6c44f0ad8c988e57a3cba08e17ad
diff --git a/core/dex_preopt_odex_install.mk b/core/dex_preopt_odex_install.mk
index 136def4..ffcd798 100644
--- a/core/dex_preopt_odex_install.mk
+++ b/core/dex_preopt_odex_install.mk
@@ -30,7 +30,7 @@
 ifdef LOCAL_UNINSTALLABLE_MODULE
 LOCAL_DEX_PREOPT :=
 endif
-ifeq (,$(strip $(built_dex)$(my_prebuilt_src_file))) # contains no java code
+ifeq (,$(strip $(built_dex)$(my_prebuilt_src_file)$(LOCAL_SOONG_DEX_JAR))) # contains no java code
 LOCAL_DEX_PREOPT :=
 endif
 # if WITH_DEXPREOPT_BOOT_IMG_ONLY=true and module is not in boot class path skip