feat(newlib): Implement getentropy() function

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

components/newlib/platform_include/sys/unistd.h

@@ -16,6 +16,7 @@ extern "C" {
 
 int truncate(const char *, off_t __length);
 int gethostname(char *__name, size_t __len);
+int getentropy(void *buffer, size_t length);
 
 #ifdef __cplusplus
 }