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)