dnl AC_VALIDATE_CACHE_SYSTEM_TYPE[(cmd)]
dnl if the cache file is inconsistent with the current host,
dnl target and build system types, execute CMD or print a default
dnl error message.
AC_DEFUN(AC_VALIDATE_CACHE_SYSTEM_TYPE, [
    AC_REQUIRE([AC_CANONICAL_SYSTEM])
    AC_MSG_CHECKING([config.cache system type])
    if { test x"${ac_cv_host_system_type+set}" = x"set" &&
         test x"$ac_cv_host_system_type" != x"$host"; } ||
       { test x"${ac_cv_build_system_type+set}" = x"set" &&
         test x"$ac_cv_build_system_type" != x"$build"; } ||
       { test x"${ac_cv_target_system_type+set}" = x"set" &&
         test x"$ac_cv_target_system_type" != x"$target"; }; then
	AC_MSG_RESULT([different])
	ifelse($#, 1, [$1],
		[AC_MSG_ERROR(["you must remove config.cache and restart configure"])])
    else
	AC_MSG_RESULT([same])
    fi
    ac_cv_host_system_type="$host"
    ac_cv_build_system_type="$build"
    ac_cv_target_system_type="$target"
])