[clang] [Clang] Fix crash in EnumDecl::getValueRange with large __int128 constants (PR #173213)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

> It looks like this regressed in clang-21, I would like to see the change that caused this to crash again. I am not sure when I will get to bisecting this though.

This bisects to 609023213d3fcc35f6ee3d47dceaf37ffa55e66b by @efriedma-quic 

https://github.com/llvm/llvm-project/pull/173213