Change with taking pointers-to-members as template arguments in C++17 [duplicate]

I know that C++17 introduced template< auto >, but the following example doesn't use it, yet still only compiles in C++17:

struct Foo
{
  int bar;
};

template< int Foo::* >
void takePtrToMember() {}

int main()
{
  takePtrToMember< &Foo::bar >(); // This works everywhere

  constexpr auto x = &Foo::bar;

  takePtrToMember< x >(); // This only works in C++17

  return 0;
}

Why doesn't it work in C++11? What has changed in C++17 so it's now allowed there?