Implement function template specialization at class scope extension in...

Implement function template specialization at class scope extension in Microsoft mode. A new AST node is introduced: ClassScopeFunctionSpecialization. This node holds a FunctionDecl that is not yet specialized; then during the class template instantiation the ClassScopeFunctionSpecialization will spawn the actual function specialization.

Example:
template <class T>
class A {
public:
  template <class U> void f(U p) {  }
  template <> void f(int p) {  } // <== class scope specialization
};

This extension is necessary to parse MSVC standard C++ headers, MFC and ATL code.
BTW, with this feature in, clang can parse (-fsyntax-only) all the MSVC 2010 standard header files without any error.

llvm-svn: 137573