Non-ICU buildfarm members, please use --without-icu

I plan to change the default build to use ICU (see patch 0001):

https://www.postgresql.org/message-id/510d284759f6e943ce15096167760b2edcb2e700.camel@j-davis.com

For those buildfarm members which do not want to build with ICU, please
specify:

  --without-icu

or builds will start breaking when I check that in.

Regards,
    Jeff Davis