#include <iostream>
  
  constexpr int f(int line)
  {
      return line;
  }
  
  #define f() f(__LINE__)
  
  int main(int argc, const char * argv[]) {
      constexpr int x = f();
      constexpr int y = f();
      
      std::cout << "x = " << x << "; y = " << y;
      return EXIT_SUCCESS;
  }

"This lack of dependency must inherently mean that it will yield the same value upon each invocation having the same set of arguments"

to be true. http://en.cppreference.com/w/cpp/language/constexpr only states:

"The constexpr specifier declares that it is possible to evaluate the value of the function or variable at compile time."

The draft of the C++ standard on my system states that as follows:

"Certain contexts require expressions that satisfy additional requirements as detailed in this sub-clause. Such expressions are called constant expressions. [ Note: Those expressions can be evaluated during translation. — end note ]"