test block system image patch at build time

After building a patch for the system image (for incremental block
OTAs), apply it to a local copy of the file and test that it succeeds.
This is an imperfect test as it's using the local client's
syspatch_host, which may differ from the syspatch library actually
used in the target build, but it's somewhat better than nothing.

Change-Id: Ic0001b0145881e2ebd4b5b36ce9b5bcebd76deb4
diff --git a/core/Makefile b/core/Makefile
index c0b2902..bae7d59 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -1136,7 +1136,8 @@
 	  $(HOST_OUT_EXECUTABLES)/make_ext4fs \
 	  $(HOST_OUT_EXECUTABLES)/simg2img \
 	  $(HOST_OUT_EXECUTABLES)/e2fsck \
-	  $(HOST_OUT_EXECUTABLES)/xdelta3
+	  $(HOST_OUT_EXECUTABLES)/xdelta3 \
+	  $(HOST_OUT_EXECUTABLES)/syspatch_host
 
 OTATOOLS := $(DISTTOOLS) \
 	  $(HOST_OUT_EXECUTABLES)/aapt