Add missing mbedtls_time_t definitions (#493)

Add missing mbedtls_time_t definitions to sample applications and the error.c
generation script.

Fixes #490.

programs/pkey/dh_server.c

@@ -30,6 +30,7 @@
 #else
 #include <stdio.h>
 #define mbedtls_printf     printf
+#define mbedtls_time_t     time_t
 #endif
 
 #if defined(MBEDTLS_AES_C) && defined(MBEDTLS_DHM_C) && \