Add LOCAL_POST_INSTALL_CMD

With this support, you can piggy-back some symlinks when a module gets
installed.
This is especially helpful if the target of the symlink doesn't exist on
the build machine.

Change-Id: I48af7a90ce67475bc49b72f94a8753b94da98edd
diff --git a/core/base_rules.mk b/core/base_rules.mk
index 8b9024a..494f75b 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -496,10 +496,12 @@
   # Define a copy rule to install the module.
   # acp and libraries that it uses can't use acp for
   # installation;  hence, LOCAL_ACP_UNAVAILABLE.
+$(LOCAL_INSTALLED_MODULE): PRIVATE_POST_INSTALL_CMD := $(LOCAL_POST_INSTALL_CMD)
 ifneq ($(LOCAL_ACP_UNAVAILABLE),true)
 $(LOCAL_INSTALLED_MODULE): $(LOCAL_BUILT_MODULE) | $(ACP)
 	@echo "Install: $@"
 	$(copy-file-to-new-target)
+	$(PRIVATE_POST_INSTALL_CMD)
 else
 $(LOCAL_INSTALLED_MODULE): $(LOCAL_BUILT_MODULE)
 	@echo "Install: $@"
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index e56180d..38c18f1 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -131,6 +131,7 @@
 LOCAL_DONT_DELETE_JAR_META_INF:=
 LOCAL_ADDITIONAL_CERTIFICATES:=
 LOCAL_PREBUILT_MODULE_FILE:=
+LOCAL_POST_INSTALL_CMD:=
 
 # Trim MAKEFILE_LIST so that $(call my-dir) doesn't need to
 # iterate over thousands of entries every time.