vvvv====from stdio.h====vvvv
#ifndef _STDIO_H
#define _STDIO_H

#ifdef __cplusplus
extern "C" {
#endif

#include <features.h>

#define __NEED_FILE
#define __NEED___isoc_va_list
#define __NEED_size_t

#if __STDC_VERSION__ < 201112L
#define __NEED_struct__IO_FILE
#endif

#if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
 || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
 || defined(_BSD_SOURCE)
#define __NEED_ssize_t
#define __NEED_off_t
#define __NEED_va_list
#endif

#include <bits/alltypes.h>

^^^====...====^^^

vvv====from alltypes.h====vvv

#if defined(__NEED_struct__IO_FILE) && !defined(__DEFINED_struct__IO_FILE)
struct _IO_FILE { char __x; };
#define __DEFINED_struct__IO_FILE
#endif

#if defined(__NEED_FILE) && !defined(__DEFINED_FILE)
typedef struct _IO_FILE FILE;
#define __DEFINED_FILE
#endif

^^^====...====^^^