test-client: Include poll.h to silence warning
test-client: Include poll.h to silence warning

Signed-off-by: Daniel Stone <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@fooishbar.org>

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