Buildfarm failure in rolenames.sql

Hi all,

Some of your may have noticed, but the buildfarm has thrown up the
following failure today:
https://buildfarm.postgresql.org/cgi-bin/show_history.pl?nm=gull&br=HEAD

The failure is the following one:
-- ALTER TABLE OWNER TO
\c -
! \connect: FATAL: could not read block 3 in file "base/16384/2662": read only 0 of 8192 bytes

I would have not bothered mentioning that as it could be perfectly be a
spurious failure, but I have actually seen the *same* failure for the
*same* block number in the *same* test on my laptop just two days ago.
So I suspect that we are up to something here. I saw the failure on my
laptop with gcc (7.3) and Debian sid, and gull is using Debian 9.4,
which is too much for a simple coincidence. The thing is hard to
reproduce only with the main regression test suite.

Thoughts?
--
Michael