Support LOCAL_PACKAGE_SPLITS.

Support LOCAL_PACKAGE_SPLITS, which accepts a list of resource lables
and generates multiple apks. The build system sets up rules to sign and
zipalign the split apks.

Bug: 16319961
Change-Id: I344b3d1c7eb158c6d0df879093d666a89870aadd
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 4fd2888..f23c4a6 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -23,6 +23,7 @@
 LOCAL_OVERRIDES_PACKAGES:=
 LOCAL_EXPORT_PACKAGE_RESOURCES:=
 LOCAL_MANIFEST_PACKAGE_NAME:=
+LOCAL_PACKAGE_SPLITS:=
 LOCAL_REQUIRED_MODULES:=
 LOCAL_ACP_UNAVAILABLE:=
 LOCAL_MODULE_TAGS:=