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
