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

fusl/src/fcntl/open.c

+#include <fcntl.h>
+#include <stdarg.h>
+#include "syscall.h"
+#include "libc.h"
+
+int open(const char *filename, int flags, ...)
+{
+        mode_t mode = 0;
+
+        if ((flags & O_CREAT) || (flags & O_TMPFILE) == O_TMPFILE) {
+                va_list ap;
+                va_start(ap, flags);
+                mode = va_arg(ap, mode_t);
+                va_end(ap);
+        }
+
+        int fd = __sys_open_cp(filename, flags, mode);
+        if (fd>=0 && (flags & O_CLOEXEC))
+                __syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
+
+        return __syscall_ret(fd);
+}
+
+LFS64(open);