Revert "cpp_dummy_build: Remove dependency on compat-1.3.h"

There is now a test that ensures all headers are included in the
cpp_dummy_build test, so we can't remove compat-1.3.h from the
cpp_dummy_build test until we remove compat-1.3.h.

This reverts commit 2b725ef.

Author: Patater

programs/test/cpp_dummy_build.cpp

@@ -44,6 +44,7 @@
 #include "mbedtls/cipher.h"
 #include "mbedtls/cipher_internal.h"
 #include "mbedtls/cmac.h"
+#include "mbedtls/compat-1.3.h"
 #include "mbedtls/ctr_drbg.h"
 #include "mbedtls/des.h"
 #include "mbedtls/dhm.h"