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);
```
Need to postpone anlysis of the ranged for loops till the actual
instantiation to avoid erroneous emission of error messages.
Differential Revision: https://reviews.llvm.org/D114560
