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/aes/aescrypt2.c

@@ -32,6 +32,7 @@
 #include <stdlib.h>
 #define mbedtls_fprintf         fprintf
 #define mbedtls_printf          printf
+#define mbedtls_exit            exit
 #define MBEDTLS_EXIT_SUCCESS    EXIT_SUCCESS
 #define MBEDTLS_EXIT_FAILURE    EXIT_FAILURE
 #endif /* MBEDTLS_PLATFORM_C */
@@ -69,7 +70,7 @@ int main( void )
     mbedtls_printf("MBEDTLS_AES_C and/or MBEDTLS_SHA256_C "
                     "and/or MBEDTLS_FS_IO and/or MBEDTLS_MD_C "
                     "not defined.\n");
-    return( 0 );
+    mbedtls_exit( 0 );
 }
 #else
 
@@ -462,6 +463,6 @@ exit:
     mbedtls_aes_free( &aes_ctx );
     mbedtls_md_free( &sha_ctx );
 
-    return( exit_code );
+    mbedtls_exit( exit_code );
 }
 #endif /* MBEDTLS_AES_C && MBEDTLS_SHA256_C && MBEDTLS_FS_IO */

programs/aes/crypt_and_hash.c

@@ -33,6 +33,7 @@
 #include <stdlib.h>
 #define mbedtls_fprintf         fprintf
 #define mbedtls_printf          printf
+#define mbedtls_exit            exit
 #define MBEDTLS_EXIT_SUCCESS    EXIT_SUCCESS
 #define MBEDTLS_EXIT_FAILURE    EXIT_FAILURE
 #endif /* MBEDTLS_PLATFORM_C */
@@ -71,7 +72,7 @@
 int main( void )
 {
     mbedtls_printf("MBEDTLS_CIPHER_C and/or MBEDTLS_MD_C and/or MBEDTLS_FS_IO not defined.\n");
-    return( 0 );
+    mbedtls_exit( 0 );
 }
 #else
 
@@ -559,6 +560,6 @@ exit:
     mbedtls_cipher_free( &cipher_ctx );
     mbedtls_md_free( &md_ctx );
 
-    return( exit_code );
+    mbedtls_exit( exit_code );
 }
 #endif /* MBEDTLS_CIPHER_C && MBEDTLS_MD_C && MBEDTLS_FS_IO */