attribute on member function type causes exception specification to be instantiated eagerly

This fails to compile: https://godbolt.org/z/e7W7raqsf
```c++
template
class CRTP {
char* foo() & noexcept(noexcept(static_cast(nullptr)->bar()))
[[clang::lifetimebound]];
};
struct S : CRTP { char* bar(); };
```
However, if `[[clang::lifetimebound]]` is commented out, it compiles fine.

I'm not sure if the code is otherwise permitted to compile by the standard or not, but this prevents the usage of `lifetimebound` with `noexcept` and [CRTP](https://en.wikipedia.org/wiki/Curiously_recurring_template_pattern), and feels like it should be avoidable.

Start by reproducing the failure from the Godbolt example, then compare the behavior with [[clang::lifetimebound]] removed. Trace how the attribute on the member function interacts with the dependent noexcept expression and CRTP instantiation. Done means the reduced example no longer eagerly instantiates the exception specification when the attribute is present.

Written by the indexing model from the issue text.