package/libbroadvoice: Broken on BR2_arc with gcc <= 4.8

Please read this bug report for details:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59049

Fixes
http://autobuild.buildroot.net/results/4a1/4a1fd92d1ce4963d3e282ea2dc8f0f6c5db4f1e1/
http://autobuild.buildroot.net/results/ce3/ce3be7d27489647a98d8932c5bcabd08c845187b/
http://autobuild.buildroot.net/results/988/988bd189bab37a03c037160d6758774d4aa6c8a0/


and many others

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>