Fix compile error that pipe is redefined

[gfphoenix78]

pipe is pre-declared as a function in system library. But, the source code in pipe.c re-define this symbol as a new type. It should be fine normally. But this behavior will cause an error in some environments, so rename this type name.

Contributor's Checklist

Here are some reminders and checklists before/when submitting your pull request, please check them:

• [ ] Make sure your Pull Request has a clear title and commit message. You can take git-commit template as a reference.
• [ ] Sign the Contributor License Agreement as prompted for your first-time contribution(One-time setup).
• [ ] Learn the coding contribution guide, including our code conventions, workflow and more.
• [ ] List your communication in the GitHub Issues or Discussions (if has or needed).
• [ ] Document changes.
• [ ] Add tests for the change
• [ ] Pass make installcheck
• [ ] Pass make -C src/test installcheck-cbdb-parallel
• [ ] Feel free to request cloudberrydb/dev team for review and approval when your PR is ready🥳