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

fusl/src/stat/fchmod.c

+#include <sys/stat.h>
+#include <errno.h>
+#include <fcntl.h>
+#include "syscall.h"
+
+void __procfdname(char *, unsigned);
+
+int fchmod(int fd, mode_t mode)
+{
+        int ret = __syscall(SYS_fchmod, fd, mode);
+        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_chmod
+        return syscall(SYS_chmod, buf, mode);
+#else
+        return syscall(SYS_fchmodat, AT_FDCWD, buf, mode);
+#endif
+}