[clang] [WIP][clang]: Implement a conditional lifetimebound_if builtin. (PR #125520)

[Haojian Wu via cfe-commits]

hokein wrote:

> auto& value = m[std::string_view(std::string())];  // Doesn't get caught

This case is supported as well, https://godbolt.org/z/KKsvd8Kx1.

https://github.com/llvm/llvm-project/pull/125520