[clang] [CIR] Upstream trivial constructor const handling (PR #164849)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

The TODO + missing-features is good enough here, the fact that upstream survived with this being this way for this long means it is probably not pressing.  But please create an issue for someone to investigate, obviously minor priority.

https://github.com/llvm/llvm-project/pull/164849