Instantiate function declarations in instantiated functions.

If a function declaration is found inside a template function as in:

    template<class T> void f() {
      void g(int x = T::v) except(T::w);
    }

it must be instantiated along with the enclosing template function,
including default arguments and exception specification.

Together with the patch committed in r240974 this implements DR1484.

Differential Revision: http://reviews.llvm.org/D11194

llvm-svn: 245810