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/ssl/ssl_fork_server.c

@@ -31,6 +31,7 @@
 #include <stdio.h>
 #define mbedtls_fprintf    fprintf
 #define mbedtls_printf     printf
+#define mbedtls_time_t     time_t
 #endif
 
 #if !defined(MBEDTLS_BIGNUM_C) || !defined(MBEDTLS_CERTS_C) ||    \