Add missing mbedtls_time_t definitions (#493)

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

Fixes #490.
diff --git a/library/error.c b/library/error.c
index debda1d..4718b51 100644
--- a/library/error.c
+++ b/library/error.c
@@ -34,6 +34,7 @@
 #include "mbedtls/platform.h"
 #else
 #define mbedtls_snprintf snprintf
+#define mbedtls_time_t   time_t
 #endif
 
 #if defined(MBEDTLS_ERROR_C)
diff --git a/programs/pkey/dh_client.c b/programs/pkey/dh_client.c
index 59c4fa8..230bf4d 100644
--- a/programs/pkey/dh_client.c
+++ b/programs/pkey/dh_client.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) && \
diff --git a/programs/pkey/dh_genprime.c b/programs/pkey/dh_genprime.c
index 6005a62..d30c73b 100644
--- a/programs/pkey/dh_genprime.c
+++ b/programs/pkey/dh_genprime.c
@@ -30,6 +30,7 @@
 #else
 #include <stdio.h>
 #define mbedtls_printf     printf
+#define mbedtls_time_t     time_t
 #endif
 
 #if !defined(MBEDTLS_BIGNUM_C) || !defined(MBEDTLS_ENTROPY_C) ||   \
diff --git a/programs/pkey/dh_server.c b/programs/pkey/dh_server.c
index 83b0b44..cb156f7 100644
--- a/programs/pkey/dh_server.c
+++ b/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) && \
diff --git a/programs/ssl/dtls_client.c b/programs/ssl/dtls_client.c
index b37eb83..14fb612 100644
--- a/programs/ssl/dtls_client.c
+++ b/programs/ssl/dtls_client.c
@@ -31,6 +31,7 @@
 #include <stdio.h>
 #define mbedtls_printf     printf
 #define mbedtls_fprintf    fprintf
+#define mbedtls_time_t     time_t
 #endif
 
 #if !defined(MBEDTLS_SSL_CLI_C) || !defined(MBEDTLS_SSL_PROTO_DTLS) ||    \
diff --git a/programs/ssl/dtls_server.c b/programs/ssl/dtls_server.c
index df0fc78..1d6eb3b 100644
--- a/programs/ssl/dtls_server.c
+++ b/programs/ssl/dtls_server.c
@@ -31,6 +31,7 @@
 #include <stdio.h>
 #define mbedtls_printf     printf
 #define mbedtls_fprintf    fprintf
+#define mbedtls_time_t     time_t
 #endif
 
 #if !defined(MBEDTLS_SSL_SRV_C) || !defined(MBEDTLS_SSL_PROTO_DTLS) ||    \
diff --git a/programs/ssl/ssl_fork_server.c b/programs/ssl/ssl_fork_server.c
index 545e2fb..363f38f 100644
--- a/programs/ssl/ssl_fork_server.c
+++ b/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) ||    \
diff --git a/scripts/data_files/error.fmt b/scripts/data_files/error.fmt
index bd6ef01..a08742c 100644
--- a/scripts/data_files/error.fmt
+++ b/scripts/data_files/error.fmt
@@ -34,6 +34,7 @@
 #include "mbedtls/platform.h"
 #else
 #define mbedtls_snprintf snprintf
+#define mbedtls_time_t   time_t
 #endif
 
 #if defined(MBEDTLS_ERROR_C)