Revert "cpp_dummy_build: Remove X.509 dependency"

This reverts commit 4c1fdb51292bbe0450dee6f7e3e794fd498635ec.
diff --git a/programs/test/cpp_dummy_build.cpp b/programs/test/cpp_dummy_build.cpp
index cc0d0e1..9cd5090 100644
--- a/programs/test/cpp_dummy_build.cpp
+++ b/programs/test/cpp_dummy_build.cpp
@@ -97,6 +97,10 @@
 #include "mbedtls/threading.h"
 #include "mbedtls/timing.h"
 #include "mbedtls/version.h"
+#include "mbedtls/x509.h"
+#include "mbedtls/x509_crl.h"
+#include "mbedtls/x509_crt.h"
+#include "mbedtls/x509_csr.h"
 #include "mbedtls/xtea.h"
 
 #if defined(MBEDTLS_PLATFORM_C)