Because the library does not have an initialisation function, we need to
rely on an automatic called-on-load mechanism, which is provided through
a compiler attribute 'constructor'.
However, as the project aims to still compile on old hard/software, we
include a check in 'configure' to ensure it works, and if not use the
legacy solution.
Note: Because we introduce a new DEFINE, the 'config.h.in' needs to be
regenerated, otherwise you may get a compilation error in wrlib. This is
done by re-running './autogen.sh'
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
