[clang] [Clang] Remove __is_nullptr (PR #99038)

[Nikolas Klauser via cfe-commits]

philnik777 wrote:

> I mostly support the removal but I'd feel more comfortable documenting the extension as deprecated in Clang 19, adding a release note warning users about it going away and what the replacement code would look like, and then remove `__is_nullptr()` in Clang 20. (edited to remove the need for a time machine as a prerequisite.)
> 
> That said, has anyone checked with Embarcadero and Microsoft as to whether they still need it supported for their STL implementations for historical reasons? That might delay the timeline or change opinions on the direction.

AFAICT MSVC never had such a trait. I don't know why it's documented that way, but the documentation is almost certainly wrong.


https://github.com/llvm/llvm-project/pull/99038