Unify the example programs' termination

This is done to account for platforms, for which we want custom behavior
upon the program termination, hence we call `mbedtls_exit()` instead of
returning from `main()`.

For the sake of consistency, introduces the modifications have been made
to the test and utility examples as well. These, while less likely to be
used in the low level environments, won't suffer from such a change.

programs/test/benchmark.c

@@ -29,6 +29,7 @@
 #include "mbedtls/platform.h"
 #else
 #include <stdio.h>
+#include <stdlib.h>
 #define mbedtls_exit       exit
 #define mbedtls_printf     printf
 #define mbedtls_snprintf   snprintf
@@ -39,7 +40,7 @@
 int main( void )
 {
     mbedtls_printf("MBEDTLS_TIMING_C not defined.\n");
-    return( 0 );
+    mbedtls_exit( 0 );
 }
 #else
 
@@ -874,7 +875,7 @@ int main( int argc, char *argv[] )
     fflush( stdout ); getchar();
 #endif
 
-    return( 0 );
+    mbedtls_exit( 0 );
 }
 
 #endif /* MBEDTLS_TIMING_C */

programs/test/selftest.c

@@ -397,6 +397,5 @@ int main( int argc, char *argv[] )
         mbedtls_exit( MBEDTLS_EXIT_FAILURE );
 
     /* return() is here to prevent compiler warnings */
-    return( MBEDTLS_EXIT_SUCCESS );
+    mbedtls_exit( MBEDTLS_EXIT_SUCCESS );
 }
-

programs/test/udp_proxy.c

@@ -40,6 +40,7 @@
 #define mbedtls_time            time
 #define mbedtls_time_t          time_t
 #define mbedtls_printf          printf
+#define mbedtls_exit            exit
 #define MBEDTLS_EXIT_SUCCESS    EXIT_SUCCESS
 #define MBEDTLS_EXIT_FAILURE    EXIT_FAILURE
 #endif /* MBEDTLS_PLATFORM_C */
@@ -48,7 +49,7 @@
 int main( void )
 {
     mbedtls_printf( "MBEDTLS_NET_C not defined.\n" );
-    return( 0 );
+    mbedtls_exit( 0 );
 }
 #else
 
@@ -142,7 +143,7 @@ static void exit_usage( const char *name, const char *value )
         mbedtls_printf( " option %s: illegal value: %s\n", name, value );
 
     mbedtls_printf( USAGE );
-    exit( 1 );
+    mbedtls_exit( 1 );
 }
 
 static void get_options( int argc, char *argv[] )
@@ -602,7 +603,7 @@ exit:
     fflush( stdout ); getchar();
 #endif
 
-    return( exit_code );
+    mbedtls_exit( exit_code );
 }
 
 #endif /* MBEDTLS_NET_C */