OK, the issue is with glibc then. The question is why did my instance of features.h revert to a version lacking this fix, and how to I get the fixed version back without manually applying the patch? It was fine until June 26. This change was the result of the equivalent of an 'apt-get update' followed by an 'apt-get upgrade'. But I have done that many times before with no problem. Our glibc is reported as being version 3.13.0-86.131, clearly more recent than 2.23.*.

We are running Ubuntu 14.04.1. Could this be some sort of problem with the Ubuntu repository?

From:        "adhemerval.zanella at linaro dot org" <sourceware-bugzilla@sourceware.org>
To:        friesens@gdls.com,
Date:        06/02/2016 08:01 PM
Subject:        [Bug math/19439] Unix98 isinf and isnan functions conflict with C++11


--- Comment #16 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
You are confusing some concepts here: first GCC and GLIBC are different
projects.  Second, an GCC update usually does not necessary update none of
GLIBC installed files. Third, distro updates does not have necessary mirror the
master changes and fixes.

This bug has been fixed on release *2.23*, so it is up to your distribution (or
you if are building our your own system) to backport the changes to the glibc

Now, if you are seeing this very issue on a GLIBC 2.23 or on master branch
(either if the package is using the release tarball or branch), now this bug
should be reopened with the information and/or a testcase to reproduce.
Otherwise this is not a GLIBC issue.

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