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/sec-tpm.hpp b/src/security/sec-tpm.hpp
index 3336a32..ec3334d 100644
--- a/src/security/sec-tpm.hpp
+++ b/src/security/sec-tpm.hpp
@@ -9,7 +9,7 @@
 #ifndef NDN_SEC_TPM_HPP
 #define NDN_SEC_TPM_HPP
 
-#include <string>
+#include "../common.hpp"
 #include "security-common.hpp"
 #include "../name.hpp"
 #include "../data.hpp"