Set PRIVATE_PREFIX when using $(transform-prebuilt-to-target)

If PRIVATE_PREFIX is unset transform-prebuilt-to-target references
$(DISPLAY) instead of $(HOST_DISPLAY) or $(TARGET_DISPLAY), which
causes unnecessary kati regenerations when the DISPLAY environment
variable changes.

Bug: 36901093
Bug: 37333696
Test: grep for $DISPLAY in out/build-${TARGET_PRODUCT}.ninja
Change-Id: Ia9802fc2b07da9b74e8f80dfdcef121408cd9817
diff --git a/core/prebuilt_internal.mk b/core/prebuilt_internal.mk
index 56e51b5..48ec340 100644
--- a/core/prebuilt_internal.mk
+++ b/core/prebuilt_internal.mk
@@ -458,6 +458,7 @@
 common_classes_jar := $(intermediates.COMMON)/classes.jar
 
 $(common_classes_jar): PRIVATE_MODULE := $(LOCAL_MODULE)
+$(common_classes_jar): PRIVATE_PREFIX := $(my_prefix)
 
 $(common_classes_jar) : $(my_src_jar)
 	$(transform-prebuilt-to-target)
@@ -469,7 +470,8 @@
 common_classes_pre_proguard_jar := $(intermediates.COMMON)/classes-pre-proguard.jar
 common_javalib_jar := $(intermediates.COMMON)/javalib.jar
 
-$(common_classes_jar) $(common_javalib_jar): PRIVATE_MODULE := $(LOCAL_MODULE)
+$(common_classes_jar) $(common_classes_pre_proguard_jar) $(common_javalib_jar): PRIVATE_MODULE := $(LOCAL_MODULE)
+$(common_classes_jar) $(common_classes_pre_proguard_jar) $(common_javalib_jar): PRIVATE_PREFIX := $(my_prefix)
 
 my_link_type := $(intermediates.COMMON)/link_type
 ifeq ($(LOCAL_SDK_VERSION),system_current)