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

fusl/include/spawn.h

+#ifndef _SPAWN_H
+#define _SPAWN_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <features.h>
+
+#define __NEED_mode_t
+#define __NEED_pid_t
+#define __NEED_sigset_t
+
+#include <bits/alltypes.h>
+
+struct sched_param;
+
+#define POSIX_SPAWN_RESETIDS 1
+#define POSIX_SPAWN_SETPGROUP 2
+#define POSIX_SPAWN_SETSIGDEF 4
+#define POSIX_SPAWN_SETSIGMASK 8
+#define POSIX_SPAWN_SETSCHEDPARAM 16
+#define POSIX_SPAWN_SETSCHEDULER 32
+
+typedef struct {
+        int __flags;
+        pid_t __pgrp;
+        sigset_t __def, __mask;
+        int __prio, __pol, __pad[16];
+} posix_spawnattr_t;
+
+typedef struct {
+        int __pad0[2];
+        void *__actions;
+        int __pad[16];
+} posix_spawn_file_actions_t;
+
+int posix_spawn(pid_t *__restrict, const char *__restrict, const posix_spawn_file_actions_t *,
+        const posix_spawnattr_t *__restrict, char *const *__restrict, char *const *__restrict);
+int posix_spawnp(pid_t *__restrict, const char *__restrict, const posix_spawn_file_actions_t *,
+        const posix_spawnattr_t *__restrict, char *const *__restrict, char *const *__restrict);
+
+int posix_spawnattr_init(posix_spawnattr_t *);
+int posix_spawnattr_destroy(posix_spawnattr_t *);
+
+int posix_spawnattr_setflags(posix_spawnattr_t *, short);
+int posix_spawnattr_getflags(const posix_spawnattr_t *__restrict, short *__restrict);
+
+int posix_spawnattr_setpgroup(posix_spawnattr_t *, pid_t);
+int posix_spawnattr_getpgroup(const posix_spawnattr_t *__restrict, pid_t *__restrict);
+
+int posix_spawnattr_setsigmask(posix_spawnattr_t *__restrict, const sigset_t *__restrict);
+int posix_spawnattr_getsigmask(const posix_spawnattr_t *__restrict, sigset_t *__restrict);
+
+int posix_spawnattr_setsigdefault(posix_spawnattr_t *__restrict, const sigset_t *__restrict);
+int posix_spawnattr_getsigdefault(const posix_spawnattr_t *__restrict, sigset_t *__restrict);
+
+int posix_spawnattr_setschedparam(posix_spawnattr_t *__restrict, const struct sched_param *__restrict);
+int posix_spawnattr_getschedparam(const posix_spawnattr_t *__restrict, struct sched_param *__restrict);
+int posix_spawnattr_setschedpolicy(posix_spawnattr_t *, int);
+int posix_spawnattr_getschedpolicy(const posix_spawnattr_t *__restrict, int *__restrict);
+
+int posix_spawn_file_actions_init(posix_spawn_file_actions_t *);
+int posix_spawn_file_actions_destroy(posix_spawn_file_actions_t *);
+
+int posix_spawn_file_actions_addopen(posix_spawn_file_actions_t *__restrict, int, const char *__restrict, int, mode_t);
+int posix_spawn_file_actions_addclose(posix_spawn_file_actions_t *, int);
+int posix_spawn_file_actions_adddup2(posix_spawn_file_actions_t *, int, int);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif