[NF] Bad handling of derived function from builtin functions

[Adrian Pop]

When handling models of this type with the NF

model Atan2  
  partial model M  "Meter 2 terminal base, 3-phase dq0" 
  protected
    function atan2 = Modelica.Math.atan2;
  end M;

  model X  
    extends M;
    parameter Real a = 1;
    parameter Real b = 2;
    parameter Real z = atan2(a, b);
  end X;

  X x;
end Atan2;

The function Atan2.X.atan2 is missing from the generated code.

I tried to fix it with PR: ​https://github.com/OpenModelica/OMCompiler/pull/2585
but that brought up other problems.

This affects the PowerSystems library.

[Adrian Pop]

Fixed by:
​https://github.com/OpenModelica/OMCompiler/pull/2585
Maybe there is a better fix, but for now this will do.