In Microsoft mode, allow template function explicit specialization at class scope.

In Microsoft mode, allow template function explicit specialization at class scope.
Necessary to parse MFC and MSVC standard lib code.

Example:
struct X {
  template<class T> void f(T) { }
  template<> void f(int) { }
}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@131347 91177308-0d34-0410-b5e6-96231b3b80d8