[clang] [Clang][ItaniumMangle] Fix infinite recursion mangling a lambda in an enable_if condition (PR #234915)

[Eugene Velesevich via cfe-commits]

TabbySqui wrote:

The `requires` case I mentioned:
```c++
template<typename T>
T inc(T a) 
    requires requires { [](int){}(a); } { return a++; }

int g = inc(0);
```

https://github.com/llvm/llvm-project/pull/234915