[clang] [clang] Disable missing definition warning on pure virtual functions (PR #74510)

[Akira Hatanaka via cfe-commits]

ahatanak wrote:

Any progress on this patch?

As we discussed in https://github.com/llvm/llvm-project/issues/74016, we should make sure clang doesn't stop emitting the warning when the definition of a pure virtual function is actually needed.

It seems to me that we shouldn't set `NeededForConstantEvaluation` or `NeedDefinition` in `Sema::MarkFunctionReferenced` to true when a pure virtual function is used in a virtual function call.

https://github.com/llvm/llvm-project/pull/74510