build: Experimental support to build using precompiled headers

This type of build needs to be explicitly enabled using --with-pch
configure option.

Change-Id: I02dc304187d54c3cf40f1d51b1b11b21f868e225
diff --git a/src/security/validator.cpp b/src/security/validator.cpp
index 62289f5..ebb8b55 100644
--- a/src/security/validator.cpp
+++ b/src/security/validator.cpp
@@ -6,6 +6,8 @@
  * See COPYING for copyright and distribution information.
  */
 
+#include "common.hpp"
+
 #include "validator.hpp"
 #include "../util/logging.hpp"