Creates a combined split-sepolicy file in merge_target_files.py.

This follows the same steps as OpenSplitPolicy() in
system/core/init/selinux.cpp on the device.

Bug: 178864050
Test: merge_target_files for R+S and S+S devices
Test: test_merge_target_files
Change-Id: Ia41a436bfda8e2cb65706122f0ff3805b99d16e1
diff --git a/core/Makefile b/core/Makefile
index a7553f0..6019452 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -4136,6 +4136,7 @@
   mkuserimg_mke2fs \
   ota_from_target_files \
   repack_bootimg \
+  secilc \
   sefcontext_compile \
   sgdisk \
   shflags \