autotools: Add a libunwind configure switch
autotools: Add a libunwind configure switch

Signed-off-by: Quentin Glidic <241385a0e41ea713327e189bce1062decf7c1eb5@sardemff7.net>

Fantu/compositor-spice,xorgy/weston,sir-murray/weston,udoprog/weston,udoprog/weston,mchalupa/weston,krezovic/weston,eyolfson/weston,eyolfson/weston,xorgy/weston,sir-murray/weston,jonnylamb/weston,giucam/weston,giucam/weston,kwm81/weston,jonnylamb/weston,Gnurou/weston,Tarnyko/weston-xdg_surface_present,mchalupa/weston,Fantu/compositor-spice,Tarnyko/weston-xdg_surface_present,Gnurou/weston,Fantu/compositor-spice,krezovic/weston,kwm81/weston