dnl AC_REMOVE_FORBIDDEN removes forbidden arguments from variables
dnl use: AC_REMOVE_FORBIDDEN(CC, [-forbid -bad-option whatever])
dnl it's all white-space separated
AC_DEFUN(AC_REMOVE_FORBIDDEN,
[ __val=$$1
  __forbid=" $2 "
  if test -n "$__val"; then
    __new=""
    ac_save_IFS=$IFS
    IFS=" 	"
    for i in $__val; do
      case "$__forbid" in
        *" $i "*) AC_MSG_WARN([found forbidden $i in $1, removing it]) ;;
	*) # Careful to not add spaces, where there were none, because otherwise
	   # libtool gets confused, if we change e.g. CXX
	   if test -z "$__new" ; then __new=$i ; else __new="$__new $i" ; fi ;;
      esac
    done
    IFS=$ac_save_IFS
    $1=$__new
  fi
])