[Clang][Sema] Abbreviated function templates do not append invented parameters to empty template parameter lists (#80864)

According to [dcl.fct] p23:
> An abbreviated function template can have a _template-head_. The
invented _template-parameters_ are appended to the
_template-parameter-list_ after the explicitly declared
_template-parameters_.

`template<>` is not a _template-head_ -- a _template-head_ must have at
least one _template-parameter_. This patch corrects our current behavior
of appending the invented template parameters to the innermost template
parameter list, regardless of whether it is empty. Example:
```
template<typename T>
struct A 
{ 
    void f(auto); 
};

template<>
void A<int>::f(auto); // ok

template<>
template<> // warning: extraneous template parameter list in template specialization
void A<int>::f(auto);
```

0 files changed, 0 insertions, 0 deletions