[Bug c++/61400] suffix return type doesn't work for template member functions with explict specialization

["yyc1992 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61400

--- Comment #2 from Yichao Yu <yyc1992 at gmail dot com> ---
Sorry I have just noticed that I forgot to include the error message...

```
gcc.cpp: In function 'int main()':
gcc.cpp:20:12: error: no matching function for call to 'A::b()'
     a.b<2>();
            ^
gcc.cpp:20:12: note: candidate is:
gcc.cpp:10:5: note: template<int i> decltype (a<i>()) A::b()
     b() -> decltype(a<i>())
     ^
gcc.cpp:10:5: note:   template argument deduction/substitution failed:
gcc.cpp: In substitution of 'template<int i> decltype (a<i>()) A::b() [with int
i = 2]':
gcc.cpp:20:12:   required from here
gcc.cpp:10:26: error: cannot call member function 'int A::a() [with int i = 2]'
without object
     b() -> decltype(a<i>())
```