[clang] [Clang] Fix crash on a forward-declared enum given an underlying type by an attribute (PR #216155)

[Shengxin Pei via cfe-commits]

TPPPP72 wrote:

This PR doesn't appear to comply with our policy on tool-generated content,
and requires additional justification for why it is valuable enough to the
project for us to review it. Please see our developer policy on
AI-generated contributions: http://llvm.org/docs/AIToolPolicy.html


https://github.com/llvm/llvm-project/pull/216155