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

fusl/include/sys/wait.h

+#ifndef _SYS_WAIT_H
+#define _SYS_WAIT_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <features.h>
+
+#define __NEED_pid_t
+#define __NEED_id_t
+#include <bits/alltypes.h>
+
+typedef enum {
+        P_ALL = 0,
+        P_PID = 1,
+        P_PGID = 2
+} idtype_t;
+
+pid_t wait (int *);
+pid_t waitpid (pid_t, int *, int );
+
+#if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
+ || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
+ || defined(_BSD_SOURCE)
+#include <signal.h>
+int waitid (idtype_t, id_t, siginfo_t *, int);
+#endif
+
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+#include <sys/resource.h>
+pid_t wait3 (int *, int, struct rusage *);
+pid_t wait4 (pid_t, int *, int, struct rusage *);
+#endif
+
+#define WNOHANG    1
+#define WUNTRACED  2
+
+#define WSTOPPED   2
+#define WEXITED    4
+#define WCONTINUED 8
+#define WNOWAIT    0x1000000
+
+#define __WNOTHREAD 0x20000000
+#define __WALL      0x40000000
+#define __WCLONE    0x80000000
+
+#define WEXITSTATUS(s) (((s) & 0xff00) >> 8)
+#define WTERMSIG(s) ((s) & 0x7f)
+#define WSTOPSIG(s) WEXITSTATUS(s)
+#define WCOREDUMP(s) ((s) & 0x80)
+#define WIFEXITED(s) (!WTERMSIG(s))
+#define WIFSTOPPED(s) ((short)((((s)&0xffff)*0x10001)>>8) > 0x7f00)
+#define WIFSIGNALED(s) (((s)&0xffff)-1U < 0xffu)
+#define WIFCONTINUED(s) ((s) == 0xffff)
+
+#ifdef __cplusplus
+}
+#endif
+#endif