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

fusl/src/fcntl/openat.c

Index: fusl/src/fcntl/openat.c
diff --git a/fusl/src/fcntl/openat.c b/fusl/src/fcntl/openat.c
new file mode 100644
index 0000000000000000000000000000000000000000..e741336c6f5587d3c4e8db596b41e48f73601a3b
--- /dev/null
+++ b/fusl/src/fcntl/openat.c
@@ -0,0 +1,20 @@
+#include <fcntl.h>
+#include <stdarg.h>
+#include "syscall.h"
+#include "libc.h"
+
+int openat(int fd, 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);
+	}
+
+	return syscall_cp(SYS_openat, fd, filename, flags|O_LARGEFILE, mode);
+}
+
+LFS64(openat);