Add LOCAL_POST_LINK_CMD.

For now we support LOCAL_POST_LINK_CMD only for static executables.
This fixed the hack of building linker which need to insert additional
step after link.

Bug: 17403674
Change-Id: Iefdfe1e3fab3a30c5d4ad701d46f931481eab572
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 34cd164..baa32e2 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -143,6 +143,7 @@
 LOCAL_DONT_DELETE_JAR_META_INF:=
 LOCAL_ADDITIONAL_CERTIFICATES:=
 LOCAL_PREBUILT_MODULE_FILE:=
+LOCAL_POST_LINK_CMD:=
 LOCAL_POST_INSTALL_CMD:=
 LOCAL_DIST_BUNDLED_BINARIES:=
 LOCAL_HAL_STATIC_LIBRARIES:=