I'd be less unhappy with this patch if the variable were not marked
GUC_REPORT. That is what gives it nontrivial cost: it's adding a couple
dozen bytes to every connection startup exchange, for data that's 100%
redundant with data already being transmitted.
The arguments that were made in favor of this patch cited its possible
use in SQL scripts, but there is no need for the variable to be marked
GUC_REPORT for that usage.
regards, tom lane