buildjson: Reduce include scope as needed

Change-Id: I8dfa600680fb253cd828f284ff217f35f76c0b46
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/bmc/buildjson.cpp b/bmc/buildjson.cpp
index 9c0bb9c..a32fbcb 100644
--- a/bmc/buildjson.cpp
+++ b/bmc/buildjson.cpp
@@ -16,6 +16,7 @@
 #include "buildjson.hpp"
 
 #include "file_handler.hpp"
+#include "general_systemd.hpp"
 
 #include <nlohmann/json.hpp>
 #include <sdbusplus/bus.hpp>