title: Doxygen's call/caller graph references missing for Fortran functions
body: <p>I try to generate a call/caller graph for a fixed-form Fortran code using Doxygen 1.8.11 using Dot (GraphViz 2.38).</p>
  
  <p>The call/caller graph works fine for subroutines, but fails (i.e. no references is drawn) for functions with a declared return value.</p>
  
  <p>i.e.  for the following code, the call to <code>MYFUNC</code> is not shown in the call graph of <code>MYSUB</code>:</p>
  
  <pre><code>  integer function MYFUNC()
      implicit none
      MYFUNC = 1
    end function
  
    subroutine MYSUB ()
      implicit NONE
      integer MYFUNC
      integer RESULT
      RESULT = MYFUNC()
    return
    end
  </code></pre>
  
  <p>Interestingly, if I remove the line <code>integer MYFUNC</code> from <code>MYSUB</code>, the call graph is drawn correctly, but the code is not valid anymore (i.e., it does not compile).</p>
  
  <p>Is there an option to include function calls in the call/caller graph?</p>