Add BUILD_ASSERT

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
diff --git a/console-server.h b/console-server.h
index c084321..ec77102 100644
--- a/console-server.h
+++ b/console-server.h
@@ -44,3 +44,7 @@
 #define container_of(ptr, type, member) \
 	((type *)((void *)((ptr) - offsetof(type, member))))
 
+#define BUILD_ASSERT(c) \
+	do { \
+		char __c[(c)?1:-1] __attribute__((unused)); \
+	} while (0)