build: make precompiled headers more useful

This can reduce the compilation time of a release
build (without tests) by more than 40%

Refs: #5212
Change-Id: I977aff0c0c7becbfee8a8b55605b81d0c014829b
diff --git a/tests/daemon/face/websocket-factory.t.cpp b/tests/daemon/face/websocket-factory.t.cpp
index 5043d87..aac1eca 100644
--- a/tests/daemon/face/websocket-factory.t.cpp
+++ b/tests/daemon/face/websocket-factory.t.cpp
@@ -28,6 +28,8 @@
 #include "face-system-fixture.hpp"
 #include "factory-test-common.hpp"
 
+#include <boost/lexical_cast.hpp>
+
 namespace nfd::tests {
 
 using face::WebSocketChannel;