[clang] [clang] Implement constexpr __builtin_bit_cast for complex types (PR #109981)

[Timm Baeder via cfe-commits]

tbaederr wrote:

I was going to add tests for floating complex types as well but I see that's rather hard and tests for floating types are rare in that file overall.

https://github.com/llvm/llvm-project/pull/109981