Move zeroize-as-memset into a config file under tests/

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>

tests/configs/config-wrapper-zeroize-memset.h

@@ -0,0 +1,31 @@
+/* mbedtls_config.h wrapper that defines mbedtls_platform_zeroize() to be
+ * memset(), so that the compile can check arguments for us.
+ * Used for testing.
+ */
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#include "mbedtls/mbedtls_config.h"
+
+#include <string.h>
+
+/* Define _ALT so we don't get the built-in implementation. The test code will
+ * also need to define MBEDTLS_TEST_DEFINES_ZEROIZE so we don't get the
+ * declaration. */
+#define MBEDTLS_PLATFORM_ZEROIZE_ALT
+
+#define mbedtls_platform_zeroize(buf, len) memset(buf, 0, len)