[clang] Mechanically convert NVPTX builtins to use TableGen (PR #122873)

[Chandler Carruth via cfe-commits]

chandlerc wrote:

Pushed an update that rebases on main, and more notably use an improved script that preserves the grouping of builtins and the comments describing them. I noticed that there were interesting and important comments here, so I reworked things so we don't lose any information.

https://github.com/llvm/llvm-project/pull/122873