Recently-introduced segfault in initdb?

I am trying to develop a small proof-of-concept patch for a proposal I
have, but recently I found that initdb started segfaulting after I did a
git pull. I used git bisect and it identified the following commit as the
first one with the problem:

1733460f0205fc6d6bbe4c14911049a918c6e073 is the first bad commit

commit 1733460f0205fc6d6bbe4c14911049a918c6e073

Author: Robert Haas <rhaas(at)postgresql(dot)org>

Date: Fri Mar 2 13:16:01 2018 -0500

postgres_fdw: Fourth attempt to stabilize regression tests.

Commit 1bc0100d270e5bcc980a0629b8726a32a497e788 added this test, and

commits 882ea509fe7a4711fe25463427a33262b873dfa1,

958e20e42d6c346ab89f6c72e4262230161d1663,

4fa396464e5fe238b7994535182f28318c61c78e tried to stabilize it. It's

still not stable, so keep trying.

The latest comment from Tom Lane is that disabling autovacuum seems

like a good strategy, but we might need to do it on more tables, hence

this patch.

Etsuro Fujita

Discussion: http://postgr.es/m/5A9928F1.2010206@lab.ntt.co.jp

:040000 040000 97d2b695bc44dd6c50ccc2c73e626ae453507299
c3e23dd08d4f9d0576401d63e375cbb3460e2d33 M contrib

bisect run success

01:01 ijmorlan(at)scsmac161$

I'm not particularly confident I've done this right but if anybody else is
having trouble with systems compiled from recent commits this might be a
starting point to look at.

Incidentally I'm working on Mac OS X 10.11.6 in case that's helpful.

And I just looked at the commit and as far as I can tell it only affects
tests, which shouldn't affect whether initdb segfaults, which makes me
think I've done something wrong.

So is anybody else finding that initdb segfaults with a newly-compiled
system?