Segfault in test suite when program pauses itself

Summary

I've noticed that the system-test suite fails when using a recent nixkpgs. It looks like the debugees hit a seg fault when trying to pause themselves.

Repro

To reproduce use the following shell:

let
  pkgs = import (builtins.fetchTarball "https://github.com/NixOS/nixpkgs/archive/545c7a31e5dedea4a6d372712a18e00ce097d462.tar.gz") {};
in
  pkgs.mkShell { buildInputs = [ pkgs.haskell.compiler.ghc925 pkgs.cabal-install pkgs.zlib pkgs.gdb ]; }

and then run cabal test system-test

Backtrace

The coredump gives the following backtrace:

(gdb) bt
#0  Socket::write (this=0x0, buf=buf@entry=0x7fffd18fbfa4 "", len=len@entry=4) at cbits/socket.cpp:36
#1  0x000000000040b644 in Response::flush (status=RESP_OKAY, this=0x7fb04f7f9b60) at cbits/stub.cpp:143
#2  Response::finish (status=RESP_OKAY, this=0x7fb04f7f9b60) at cbits/stub.cpp:209
#3  pause_mutator () at cbits/stub.cpp:235
#4  0x0000000000407394 in ghczmdebugzmstubzm0zi4zi0zi0zminplace_GHCziDebugziStub_pause1_info ()
#5  0x0000000000000000 in ?? ()