The build fails with slibtool while GNU libtool hide the issue
by silently ignoring -no-undefined.
ax_pthread.m4 is sourced from:
e68e8f6f62/m4/ax_pthread.m4
Downstream issue: https://bugs.gentoo.org/780027
Signed-off-by: orbea <orbea@riseup.net>
Acked-by: Frediano Ziglio <freddy77@gmail.com>
