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

fusl/include/grp.h

+#ifndef _GRP_H
+#define _GRP_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <features.h>
+
+#define __NEED_size_t
+#define __NEED_gid_t
+
+#ifdef _GNU_SOURCE
+#define __NEED_FILE
+#endif
+
+#include <bits/alltypes.h>
+
+struct group
+{
+        char *gr_name;
+        char *gr_passwd;
+        gid_t gr_gid;
+        char **gr_mem;
+};
+
+struct group  *getgrgid(gid_t);
+struct group  *getgrnam(const char *);
+
+int getgrgid_r(gid_t, struct group *, char *, size_t, struct group **);
+int getgrnam_r(const char *, struct group *, char *, size_t, struct group **);
+
+struct group  *getgrent(void);
+void           endgrent(void);
+void           setgrent(void);
+
+#ifdef _GNU_SOURCE
+struct group  *fgetgrent(FILE *stream);
+int putgrent(const struct group *, FILE *);
+#endif
+
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+int getgrouplist(const char *, gid_t, gid_t *, int *);
+int setgroups(size_t, const gid_t *);
+int initgroups(const char *, gid_t);
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif