ac_subst_dir

This macro substitutes (with AC_SUBST) VARNAME with the expansion of itself or the DIR variable if specified, taking care of fixing up ${prefix} and such.

Side effect: VARNAME is replaced with the expansion.

AC_SUBST_DIR bases on Alexandre Oliva's AC_DEFINE_DIR macro.

Examples:

    AC_SUBST_DIR(DATADIR)

AC_DEFUN([AC_SUBST_DIR], [
        ifelse($2,,,$1="[$]$2")
        $1=`(
            test "x$prefix" = xNONE && prefix="$ac_default_prefix"
            test "x$exec_prefix" = xNONE && exec_prefix="${prefix}"
            eval echo \""[$]$1"\"
        )`
        AC_SUBST($1)
])