package/autoconf-archive: fix ax_tls syntax error

The ax_tls.m4 serial 11 procude a syntax error
in configure scripts.

Fixes:
http://autobuild.buildroot.net/results/619/619339810617212a667fe72278ec727ee992ffbf/



Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>