feat(newlib): Implement getentropy() function

Closes https://github.com/espressif/esp-idf/issues/11963

components/newlib/getentropy.c

@@ -0,0 +1,30 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <sys/random.h>
+#include <errno.h>
+
+int getentropy(void *buffer, size_t length)
+{
+    ssize_t ret;
+
+    if (buffer == NULL) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    if (length > 256) {
+        errno = EIO;
+        return -1;
+    }
+
+    ret = getrandom(buffer, length, 0);
+    if (ret == -1) {
+        return -1;
+    }
+
+    return 0;
+}