Add a "fork" of musl as //fusl.

fusl/src/internal/stdio_impl.h

+#ifndef _STDIO_IMPL_H
+#define _STDIO_IMPL_H
+
+#include <stdio.h>
+#include "syscall.h"
+#include "libc.h"
+
+#define UNGET 8
+
+#define FFINALLOCK(f) ((f)->lock>=0 ? __lockfile((f)) : 0)
+#define FLOCK(f) int __need_unlock = ((f)->lock>=0 ? __lockfile((f)) : 0)
+#define FUNLOCK(f) if (__need_unlock) __unlockfile((f)); else
+
+#define F_PERM 1
+#define F_NORD 4
+#define F_NOWR 8
+#define F_EOF 16
+#define F_ERR 32
+#define F_SVB 64
+#define F_APP 128
+
+struct _IO_FILE {
+        unsigned flags;
+        unsigned char *rpos, *rend;
+        int (*close)(FILE *);
+        unsigned char *wend, *wpos;
+        unsigned char *mustbezero_1;
+        unsigned char *wbase;
+        size_t (*read)(FILE *, unsigned char *, size_t);
+        size_t (*write)(FILE *, const unsigned char *, size_t);
+        off_t (*seek)(FILE *, off_t, int);
+        unsigned char *buf;
+        size_t buf_size;
+        FILE *prev, *next;
+        int fd;
+        int pipe_pid;
+        long lockcount;
+        short dummy3;
+        signed char mode;
+        signed char lbf;
+        volatile int lock;
+        volatile int waiters;
+        void *cookie;
+        off_t off;
+        char *getln_buf;
+        void *mustbezero_2;
+        unsigned char *shend;
+        off_t shlim, shcnt;
+        FILE *prev_locked, *next_locked;
+        struct __locale_struct *locale;
+};
+
+size_t __stdio_read(FILE *, unsigned char *, size_t);
+size_t __stdio_write(FILE *, const unsigned char *, size_t);
+size_t __stdout_write(FILE *, const unsigned char *, size_t);
+off_t __stdio_seek(FILE *, off_t, int);
+int __stdio_close(FILE *);
+
+size_t __string_read(FILE *, unsigned char *, size_t);
+
+int __toread(FILE *);
+int __towrite(FILE *);
+
+#if defined(__PIC__) && (100*__GNUC__+__GNUC_MINOR__ >= 303)
+__attribute__((visibility("protected")))
+#endif
+int __overflow(FILE *, int), __uflow(FILE *);
+
+int __fseeko(FILE *, off_t, int);
+int __fseeko_unlocked(FILE *, off_t, int);
+off_t __ftello(FILE *);
+off_t __ftello_unlocked(FILE *);
+size_t __fwritex(const unsigned char *, size_t, FILE *);
+int __putc_unlocked(int, FILE *);
+
+FILE *__fdopen(int, const char *);
+int __fmodeflags(const char *);
+
+FILE *__ofl_add(FILE *f);
+FILE **__ofl_lock(void);
+void __ofl_unlock(void);
+
+#define feof(f) ((f)->flags & F_EOF)
+#define ferror(f) ((f)->flags & F_ERR)
+
+#define getc_unlocked(f) \
+        ( ((f)->rpos < (f)->rend) ? *(f)->rpos++ : __uflow((f)) )
+
+#define putc_unlocked(c, f) ( ((c)!=(f)->lbf && (f)->wpos<(f)->wend) \
+        ? *(f)->wpos++ = (c) : __overflow((f),(c)) )
+
+/* Caller-allocated FILE * operations */
+FILE *__fopen_rb_ca(const char *, FILE *, unsigned char *, size_t);
+int __fclose_ca(FILE *);
+
+#endif