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

fusl/src/unistd/fchown.c

Index: fusl/src/unistd/fchown.c
diff --git a/fusl/src/unistd/fchown.c b/fusl/src/unistd/fchown.c
new file mode 100644
index 0000000000000000000000000000000000000000..03459849e50a3436d5bec51a4763375e05c4796d
--- /dev/null
+++ b/fusl/src/unistd/fchown.c
@@ -0,0 +1,22 @@
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include "syscall.h"
+
+void __procfdname(char *, unsigned);
+
+int fchown(int fd, uid_t uid, gid_t gid)
+{
+	int ret = __syscall(SYS_fchown, fd, uid, gid);
+	if (ret != -EBADF || __syscall(SYS_fcntl, fd, F_GETFD) < 0)
+		return __syscall_ret(ret);
+
+	char buf[15+3*sizeof(int)];
+	__procfdname(buf, fd);
+#ifdef SYS_chown
+	return syscall(SYS_chown, buf, uid, gid);
+#else
+	return syscall(SYS_fchownat, AT_FDCWD, buf, uid, gid);
+#endif
+
+}