[libc] Add a few missing fcntl.h macro. (#226810)

* Add a few POSIX-specified symbolic constants to `<fcntl.h>`:
`O_RSYNC`,
  `AT_SYMLINK_FOLLOW`, and `F_DUPFD_CLOEXEC`.
* Don't add `_CLOFORK` variants, since those are not supported by Linux.
* List the constants in the `fcntl.yaml` file for posterity.

GitOrigin-RevId: b5a51c5b670728f0b3bcb3d31bc063821cbcfb4b