5261 libm should stop using synonyms.h

*** 24,35 ****
  /*
   * Copyright 2005 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
! #pragma weak nextafter = __nextafter
! #pragma weak _nextafter = __nextafter
  
  #include "libm.h"
  #include <float.h>              /* DBL_MIN */
  
  double
--- 24,35 ----
  /*
   * Copyright 2005 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
! #pragma weak __nextafter = nextafter
! #pragma weak _nextafter = nextafter
  
  #include "libm.h"
  #include <float.h>              /* DBL_MIN */
  
  double