MBEDTLS_ERROR_STRERROR_DUMMY macro

\def MBEDTLS_ERROR_STRERROR_DUMMY Enable a dummy error function to make use of mbedtls_strerror() in third party libraries easier when MBEDTLS_ERROR_C is disabled (no effect when MBEDTLS_ERROR_C is enabled). You can safely disable this if MBEDTLS_ERROR_C is enabled, or if you're not using mbedtls_strerror() or error_strerror() in your application. Disable if you run into name conflicts and want to really remove the mbedtls_strerror()