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

fusl/include/sys/uio.h

+#ifndef _SYS_UIO_H
+#define _SYS_UIO_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <features.h>
+
+#define __NEED_size_t
+#define __NEED_ssize_t
+#define __NEED_struct_iovec
+
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+#define __NEED_off_t
+#endif
+
+#ifdef _GNU_SOURCE
+#define __NEED_pid_t
+#endif
+
+#include <bits/alltypes.h>
+
+#define UIO_MAXIOV 1024
+
+ssize_t readv (int, const struct iovec *, int);
+ssize_t writev (int, const struct iovec *, int);
+
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+ssize_t preadv (int, const struct iovec *, int, off_t);
+ssize_t pwritev (int, const struct iovec *, int, off_t);
+#if defined(_LARGEFILE64_SOURCE) || defined(_GNU_SOURCE)
+#define preadv64 preadv
+#define pwritev64 pwritev
+#define off64_t off_t
+#endif
+#endif
+
+#ifdef _GNU_SOURCE
+ssize_t process_vm_writev(pid_t, const struct iovec *, unsigned long, const struct iovec *, unsigned long, unsigned long);
+ssize_t process_vm_readv(pid_t, const struct iovec *, unsigned long, const struct iovec *, unsigned long, unsigned long);
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif