5261 libm should stop using synonyms.h

*** 25,35 ****
  /*
   * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
! #pragma weak cbrtf = __cbrtf
  
  #include "libm.h"
  
  float
  cbrtf(float x) {
--- 25,35 ----
  /*
   * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
! #pragma weak __cbrtf = cbrtf
  
  #include "libm.h"
  
  float
  cbrtf(float x) {