dnl Copyright (C) 2004-2008 Kim Woelders
dnl This code is public domain and can be freely used or copied.
dnl Originally snatched from somewhere...

dnl Macro for checking if the compiler supports __attribute__

dnl Usage: AC_C___ATTRIBUTE__

dnl Call AC_DEFINE for HAVE___ATTRIBUTE__ and __UNUSED__.
dnl If the compiler supports __attribute__, HAVE___ATTRIBUTE__ is
dnl defined to 1 and __UNUSED__ is defined to __attribute__((unused))
dnl otherwise, HAVE___ATTRIBUTE__ is not defined and __UNUSED__ is
dnl defined to nothing.

AC_DEFUN([AC_C___ATTRIBUTE__],
[
  AC_MSG_CHECKING(for __attribute__)
  AC_CACHE_VAL(ac_cv___attribute__, [
  AC_TRY_COMPILE([#include <stdlib.h>],
  [int func(int x); int foo(int x __attribute__ ((unused))) { exit(1); }],
  ac_cv___attribute__=yes, ac_cv___attribute__=no)])
  if test "$ac_cv___attribute__" = "yes"; then
    AC_DEFINE(HAVE___ATTRIBUTE__, 1, [Define to 1 if your compiler has __attribute__])
    AC_DEFINE(__UNUSED__, __attribute__((unused)), [Macro declaring a function argument to be unused])
  else
    AC_DEFINE(__UNUSED__, , [Macro declaring a function argument to be unused])
  fi
  AC_MSG_RESULT($ac_cv___attribute__)
])