Fixes SSL sample apps for non-default configs

Fixes the SSL sample applications to build for the non-default configs
which don't build if MBEDTLS_PLATFORM_C isn't defined.
diff --git a/programs/test/udp_proxy.c b/programs/test/udp_proxy.c
index eb8d29e..b698c78 100644
--- a/programs/test/udp_proxy.c
+++ b/programs/test/udp_proxy.c
@@ -34,11 +34,15 @@
 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
 #else
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#define mbedtls_time       time
+#define mbedtls_time_t     time_t
 #define mbedtls_printf     printf
 #endif
 
 #if !defined(MBEDTLS_NET_C)
-#include <stdio.h>
 int main( void )
 {
     mbedtls_printf( "MBEDTLS_NET_C not defined.\n" );
@@ -50,10 +54,7 @@
 #include "mbedtls/error.h"
 #include "mbedtls/ssl.h"
 
-#include <stdio.h>
-#include <stdlib.h>
 #include <string.h>
-#include <time.h>
 
 /* For select() */
 #if (defined(_WIN32) || defined(_WIN32_WCE)) && !defined(EFIX64) && \