[clang] [clang] Fix crash on invalid decltype specifier (PR #224844)

[Rajin Khan via cfe-commits]

rajin-khan wrote:

Closing this because I used AI assistance while investigating and preparing the patch, and LLVM's AI Tool Use Policy prohibits AI-assisted fixes for issues labeled . I found the policy through the first-contributor notice after opening the PR. Sorry for the noise.

https://github.com/llvm/llvm-project/pull/224844