[Issue2229] make check 14 of 35 tests failed

[Mark H Weaver]

[I wanted to add this to <https://bugs.gnupg.org/gnupg/issue2229>,
but I wasn't able to find the email address where I should send it.]

We've run into this problem in GNU Guix.  Here's the report in our bug
tracker:

  https://debbugs.gnu.org/22558

A few observations:

* The problem mostly only occurs on x86_64 systems.  On our build farm,
  gnupg-2.1.11 failed to build 8 times before it finally succeeded.  On
  our other supported architectures (i686, armhf, and mips64el), it
  succeeded on the first try.

* Sometimes there are 14 failures, and sometimes there's only 1 failure
  (gpgtar.test).

* Although we perform builds within an isolated build container, the
  problem tends to happen on some systems and not others.  Ludovic
  Courtès reported building gnupg-2.1.11 three times on his x86_64
  laptop, and that it succeeded all three times.  Other users have
  reported consistent build failures.

* One of the core Guix developers who consistently gets 14 failures did
  a git bisect, and found that the problem was apparently introduced in
  commit ee87c653bf.

     Regards,
       Mark