Support "LOCAL_SDK_VERSION := system_current"

A module can declare "LOCAL_SDK_VERSION := system_current" to build
against the android system stubs generated from source.
For now this is only supported in platform build.

Change-Id: I1e9bbd159886bc0ea3a02b1dc4cbcb1a56e9cb15
diff --git a/core/base_rules.mk b/core/base_rules.mk
index 2984d9d..f40eae7 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -207,12 +207,12 @@
 aidl_preprocess_import :=
 LOCAL_SDK_VERSION:=$(strip $(LOCAL_SDK_VERSION))
 ifdef LOCAL_SDK_VERSION
-ifeq ($(LOCAL_SDK_VERSION)$(TARGET_BUILD_APPS),current)
+ifneq ($(filter current system_current, $(LOCAL_SDK_VERSION)$(TARGET_BUILD_APPS)),)
   # LOCAL_SDK_VERSION is current and no TARGET_BUILD_APPS
   aidl_preprocess_import := $(TARGET_OUT_COMMON_INTERMEDIATES)/framework.aidl
 else
   aidl_preprocess_import := $(HISTORICAL_SDK_VERSIONS_ROOT)/$(LOCAL_SDK_VERSION)/framework.aidl
-endif # !current
+endif # not current or system_current
 else
 # build against the platform.
 LOCAL_AIDL_INCLUDES += $(FRAMEWORKS_BASE_JAVA_SRC_DIRS)
@@ -395,9 +395,11 @@
 ifeq ($(LOCAL_SDK_VERSION)$(TARGET_BUILD_APPS),current)
 # LOCAL_SDK_VERSION is current and no TARGET_BUILD_APPS.
 $(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_BOOTCLASSPATH := -bootclasspath $(call java-lib-files,android_stubs_current)
+else ifeq ($(LOCAL_SDK_VERSION)$(TARGET_BUILD_APPS),system_current)
+$(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_BOOTCLASSPATH := -bootclasspath $(call java-lib-files,android_system_stubs_current)
 else
 $(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_BOOTCLASSPATH := -bootclasspath $(call java-lib-files,sdk_v$(LOCAL_SDK_VERSION))
-endif # current
+endif # current or system_current
 endif # LOCAL_SDK_VERSION
 endif # TARGET_
 $(LOCAL_INTERMEDIATE_TARGETS): PRIVATE_RESOURCE_DIR := $(LOCAL_RESOURCE_DIR)