erroneous nonblocking attribute warning with two layers of template functions

using clang 22.1.0 and `-Wfunction-effects`:

```cpp
template
int f1() noexcept [[clang::nonblocking]]
{
return 0;
}

template
auto f2(T a = f1()) noexcept [[clang::nonblocking]]
{
return a;
}

int main(int argc, char const* argv[])
{
return f2(argc);
}
```

```
nonblocking.cpp:8:32: warning: function with
'nonblocking' attribute must not call non-'nonblocking' expression
[-Wfunction-effects]
8 | auto f2(T a = f1()) noexcept [[clang::nonblocking]]
| ^
```

(also thinking that the warning message could be improved from its current triple-negative formulation: "NOT call NON-'NONblocking'")

Start by compiling the supplied nonblocking.cpp reproducer with Clang 22.1.0 and -Wfunction-effects. Trace how the warning handles the default argument f1() across the two template functions. Done means the erroneous warning is resolved, with the diagnostic wording considered for clarity.

Written by the indexing model from the issue text.