[clang] Fix false positive of [[clang::require_explicit_initialization]] on copy/move constructors (PR #126553)

[Aaron Ballman via cfe-commits]

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

LGTM, but waiting for @hokein to have a chance to approve as well.

https://github.com/llvm/llvm-project/pull/126553