[clang] [Clang] Instantiate functions from constant evaluation. (PR #205557)

[Corentin Jabot via cfe-commits]

cor3ntin wrote:

@jyknight right, there are more work to be done to fix all of the issues - i do not think it needs to be in that PR - they are related but distinct issues

https://github.com/llvm/llvm-project/pull/205557