5261 libm should stop using synonyms.h

*** 28,38 ****
  
          .file "isnanl.s"
  
  #include "libm.h"
  LIBM_ANSI_PRAGMA_WEAK(isnanl,function)
- #include "libm_synonyms.h"
  
          ENTRY(isnanl)
          movl    12(%esp),%eax           / ax <-- sign bit and exp
          andl    $0x00007fff,%eax
          jz      .not_nan                / jump if exp is all 0
--- 28,37 ----