[clang] [Clang] Defer the instantiation of explicit-specifier until constraint checking completes (PR #70548)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 commented:

Thank you for working on this! Some nit comments, hope you don't mind.
(Also invited some clang folks to have a detailed look at this. :=)


https://github.com/llvm/llvm-project/pull/70548