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/droiddoc.mk b/core/droiddoc.mk
index 655af9b..5f0dc6f 100644
--- a/core/droiddoc.mk
+++ b/core/droiddoc.mk
@@ -64,6 +64,9 @@
     # Use android_stubs_current if LOCAL_SDK_VERSION is current and no TARGET_BUILD_APPS.
     LOCAL_JAVA_LIBRARIES := android_stubs_current $(LOCAL_JAVA_LIBRARIES)
     $(full_target): PRIVATE_BOOTCLASSPATH := $(call java-lib-files, android_stubs_current)
+  else ifeq ($(LOCAL_SDK_VERSION)$(TARGET_BUILD_APPS),system_current)
+    LOCAL_JAVA_LIBRARIES := android_system_stubs_current $(LOCAL_JAVA_LIBRARIES)
+    $(full_target): PRIVATE_BOOTCLASSPATH := $(call java-lib-files, android_system_stubs_current)
   else
     LOCAL_JAVA_LIBRARIES := sdk_v$(LOCAL_SDK_VERSION) $(LOCAL_JAVA_LIBRARIES)
     $(full_target): PRIVATE_BOOTCLASSPATH := $(call java-lib-files, sdk_v$(LOCAL_SDK_VERSION))