[clang] [clang]Avoid diagnose invalid consteval call for invalid function decl (PR #68646)

[via cfe-commits]

================
@@ -358,6 +358,8 @@ Bug Fixes in This Version
   Fixes (`#67690 <https://github.com/llvm/llvm-project/issues/67690>`_)
 - Fixes a ``clang-17`` regression where ``LLVM_UNREACHABLE_OPTIMIZE=OFF``
   cannot be used with ``Release`` mode builds. (`#68237 <https://github.com/llvm/llvm-project/issues/68237>`_).
+- Fix crash in evaluating ``constexpr`` value for invalid template function.
----------------
cor3ntin wrote:

```suggestion
- Fix crash when evaluating an invalid immediate function template.
```

https://github.com/llvm/llvm-project/pull/68646