[clang] [Clang][Sema] Do not perform type conversion before computing result type of `x ? : y` in C++ (PR #108837)

[Yanzuo Liu via cfe-commits]

zwuis wrote:

> I'm also concerned about the constexpr support being 'FIXME', it seems that this should just 'work' unless something odd is happening.

Sorry I forgot the restriction of constexpr function in C++11. Fixed.

https://github.com/llvm/llvm-project/pull/108837