No way to override default localstatedir in configure.ac

[Basin Ilya]

Autoconf has `AC_PREFIX_DEFAULT` macro to override default prefix. User
can still pass a different --prefix on ./configure command line.

Other "Installation directory options" cannot be changed.

>From general.m4:

    AC_SUBST([localstatedir],  ['${prefix}/var'])dnl
    ...
      case $ac_dashdash$ac_option in
      -localstatedir | --localstatedir | --localstatedi | --localstated \
      | --localstate | --localstat | --localsta | --localst | --locals)
        ac_prev=localstatedir ;;


There's no way to assign a different value to localstatedir after
'${prefix}/var', but before arguments are parsed.

autoconf version 2.69