This issue will start impacting m4 in Red Hat Enterprise Linux 9 once we switch to glibc 2.34.

[[[EDIT No longer applicable, a regular build with suffice EDIT]]]
You can test a fix before glibc 2.34 is merged using this command:

koji -p stream build --scratch c9s-build-side-102-stack-gate git+https://gitlab.com/redhat/centos-stream/rpms/m4#origin/c9s

+++ This bug was initially created as a clone of Bug #1943033 +++

Your package fails to build with the newest upcoming autoconf-2.71, which is part of a wide Fedora change. Please see the attached copr: https://copr.fedorainfracloud.org/coprs/odubaj/autoconf-2.70/packages/. More information about testing your package when building with autoconf available here: https://fedoraproject.org/wiki/Changes/Autoconf_271#How_To_Test

--- Additional comment from Vitezslav Crhonek on 2021-03-29 13:08:41 CEST ---

This doesn't look like fail because autoconf, but because of recent change in glibc. It's already discussed at m4 upstream
mailing list and also at [1].

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=20305

--- Additional comment from Ondrej Dubaj on 2021-04-12 09:13:10 CEST ---

Gentle ping.

--- Additional comment from Ernestas on 2021-04-13 11:25:58 CEST ---

There’s no obvious interest upstream, so maybe this should be reassigned to glibc or another bug should be created there for extra eyes.

--- Additional comment from Florian Weimer on 2021-04-14 09:53:51 CEST ---

There is currently no plan to revert the glibc change. m4 has to be fixed. Thanks.

--- Additional comment from Vitezslav Crhonek on 2021-05-10 13:20:34 CEST ---

(In reply to Ernestas from comment #3)
> There’s no obvious interest upstream, so maybe this should be reassigned to
> glibc or another bug should be created there for extra eyes.

Upstream has released 1.4.18b that fixes this issue (inherits the fix from gnulib).
I've created COPR repo with that release:
https://copr.fedorainfracloud.org/coprs/vcrhonek/m4-test/

Stable 1.4.19 is going to be released later this month.