frexpl: avoid bug on AIX

[Bruno Haible]

The function frexpl() on AIX doesn't return reasonable values at all. It has
to be disabled in a configure test. I'm applying this:

2007-03-25  Bruno Haible  <address@hidden>

        * m4/frexpl.m4 (gl_FUNC_FREXPL_WORKS): Test also finite numbers.

*** m4/frexpl.m4        25 Mar 2007 21:35:38 -0000      1.2
--- m4/frexpl.m4        25 Mar 2007 22:17:45 -0000
***************
*** 58,65 ****
    fi
  ])
  
! dnl Test whether frexpl() works also on infinite numbers (this fails e.g. on
! dnl IRIX 6.5).
  AC_DEFUN([gl_FUNC_FREXPL_WORKS],
  [
    AC_REQUIRE([AC_PROG_CC])
--- 58,65 ----
    fi
  ])
  
! dnl Test whether frexpl() works on finite numbers (this fails on AIX 5.1) and
! dnl also on infinite numbers (this fails e.g. on IRIX 6.5).
  AC_DEFUN([gl_FUNC_FREXPL_WORKS],
  [
    AC_REQUIRE([AC_PROG_CC])
***************
*** 71,76 ****
--- 71,84 ----
  int main()
  {
    volatile long double x;
+   /* Test on finite numbers.  */
+   {
+     int exp = -9999;
+     x = 16.0L;
+     frexpl (x, &exp);
+     if (exp != 5)
+       return 1;
+   }
    /* Test on infinite numbers.  */
    {
      x = 1.0L / 0.0L;
***************
*** 82,89 ****
    return 0;
  }], [gl_cv_func_frexpl_works=yes], [gl_cv_func_frexpl_works=no],
        [case "$host_os" in
!          irix*) gl_cv_func_frexpl_works="guessing no";;
!          *)     gl_cv_func_frexpl_works="guessing yes";;
         esac
        ])
      ])
--- 90,97 ----
    return 0;
  }], [gl_cv_func_frexpl_works=yes], [gl_cv_func_frexpl_works=no],
        [case "$host_os" in
!          aix* | irix*) gl_cv_func_frexpl_works="guessing no";;
!          *)            gl_cv_func_frexpl_works="guessing yes";;
         esac
        ])
      ])