dnl EXTRA_COMPILE_WARNINGS
dnl Turn on many useful compiler warnings
dnl For now, only works on GCC
AC_DEFUN([EXTRA_COMPILE_WARNINGS],[
    dnl ******************************
    dnl More compiler warnings
    dnl ******************************

    AC_ARG_ENABLE(compile-warnings,
                  AC_HELP_STRING([--enable-compile-warnings=@<:@no/minimum/yes/maximum/error@:>@],
                                 [Turn on compiler warnings]),,
                  [enable_compile_warnings="m4_default([$1],[yes])"])

    warnCFLAGS=
    if test "x$GCC" != xyes; then
	enable_compile_warnings=no
    fi

    warning_flags=
    realsave_CFLAGS="$CFLAGS"

    case "$enable_compile_warnings" in
    no)
	warning_flags=
	;;
    minimum)
	warning_flags="-Wall"
	;;
    yes)
	warning_flags="-Wall -Wmissing-prototypes"
	;;
    maximum|error)
	warning_flags="-Wall -Wmissing-prototypes -Wnested-externs -Wpointer-arith"
	CFLAGS="$warning_flags $CFLAGS"
	for option in -Wno-sign-compare; do
		SAVE_CFLAGS="$CFLAGS"
		CFLAGS="$CFLAGS $option"
		AC_MSG_CHECKING([whether gcc understands $option])
		AC_TRY_COMPILE([], [],
			has_option=yes,
			has_option=no,)
		CFLAGS="$SAVE_CFLAGS"
		AC_MSG_RESULT($has_option)
		if test $has_option = yes; then
		  warning_flags="$warning_flags $option"
		fi
		unset has_option
		unset SAVE_CFLAGS
	done
	unset option
	if test "$enable_compile_warnings" = "error" ; then
	    warning_flags="$warning_flags -Werror"
	fi
	;;
    *)
	AC_MSG_ERROR(Unknown argument '$enable_compile_warnings' to --enable-compile-warnings)
	;;
    esac
    CFLAGS="$realsave_CFLAGS"
    AC_MSG_CHECKING(what warning flags to pass to the C compiler)
    AC_MSG_RESULT($warning_flags)

    AC_ARG_ENABLE(iso-c,
                  AC_HELP_STRING([--enable-iso-c],
                                 [Try to warn if code is not ISO C ]),,
                  [enable_iso_c=no])

    AC_MSG_CHECKING(what language compliance flags to pass to the C compiler)
    complCFLAGS=
    if test "x$enable_iso_c" != "xno"; then
	if test "x$GCC" = "xyes"; then
	case " $CFLAGS " in
	    *[\ \	]-ansi[\ \	]*) ;;
	    *) complCFLAGS="$complCFLAGS -ansi" ;;
	esac
	case " $CFLAGS " in
	    *[\ \	]-pedantic[\ \	]*) ;;
	    *) complCFLAGS="$complCFLAGS -pedantic" ;;
	esac
	fi
    fi
    AC_MSG_RESULT($complCFLAGS)

    WARN_CFLAGS="$warning_flags $complCFLAGS"
    AC_SUBST(WARN_CFLAGS)
])