[clang] [clang] [SemaCXX] Implement CWG2627 Bit-fields and narrowing conversions (PR #78112)

[A. Jiang via cfe-commits]

frederick-vs-ja wrote:

> Should this be a SFINAE-able error before C++23? (It isn't currently)

I believe this should (in C++11 and later modes).

https://github.com/llvm/llvm-project/pull/78112