libtar: store SELinux file context in tar archives

* Using RedHat's "RHT.security.selinux=" tag in extended
  tar header (type 'x')

Signed-off-by: Vojtech Bocek <vbocek@gmail.com>

Change-Id: I102e492e4fa5b8a08fae4d34eb36386862509b4d
diff --git a/libtar/Android.mk b/libtar/Android.mk
index b73a41f..7e0fafb 100644
--- a/libtar/Android.mk
+++ b/libtar/Android.mk
@@ -11,5 +11,11 @@
 					external/zlib
 LOCAL_SHARED_LIBRARIES += libz libc
 
+ifneq ($(wildcard external/libselinux/Android.mk),)
+	LOCAL_C_INCLUDES += external/libselinux/include
+	LOCAL_SHARED_LIBRARIES += libselinux
+	LOCAL_CFLAGS += -DHAVE_SELINUX
+endif
+
 include $(BUILD_SHARED_LIBRARY)