Catch nonexistent BOARD_SEPOLICY_UNION policy files.

Added a new check to make sure that all listed
BOARD_SEPOLICY_UNION files are located somewhere
in the listed BOARD_SEPOLICY_DIRS locations. The
build will error out otherwise.

Change-Id: Icc5febc5fe5a7cccb90ac5b83e6289c2aa5bf069
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>

Android.mk

@@ -50,6 +50,15 @@ $(foreach pf, $(BOARD_SEPOLICY_REPLACE), \
   ) \
 )
 
+# Quick edge case error detection for BOARD_SEPOLICY_UNION.
+# This ensures that a requested union file exists somewhere
+# in one of the listed BOARD_SEPOLICY_DIRS.
+$(foreach pf, $(BOARD_SEPOLICY_UNION), \
+  $(if $(filter 0, $(words $(wildcard $(addsuffix /$(pf), $(BOARD_SEPOLICY_DIRS))))), \
+    $(error No sepolicy file found for $(pf) in $(BOARD_SEPOLICY_DIRS)), \
+  ) \
+)
+
 # Builds paths for all requested policy files w.r.t
 # both BOARD_SEPOLICY_REPLACE and BOARD_SEPOLICY_UNION
 # product variables.