[clang] [Clang] Reconsider the timing of instantiation of local constexpr lambdas (PR #98758)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

Finally, I decide to revert #95660 and close this PR for now.

Regarding issues associated with #95660, I realized they are actually part of a bigger problem in constant evaluation. As discussed in #59966, it might be beneficial to implement on-demand template instantiation for constant evaluation. That way, we don't have to touch the logic of deferral instantiation in `MarkFunctionReferenced()`, (which probably can be removed then) and we could instantiate those local lambdas before evaluation.

https://github.com/llvm/llvm-project/pull/98758