build: fix setuid check
build: fix setuid check

At least in some shells test needs 3 arguments for string comparison

if test $foo=yes ...

will always be true.

if test $foo = yes ...

will perform a string comparison.

Signed-off-by: Derek Foreman <2f97e0f0bc172406aab8ccd42dab54c95bab8759@osg.samsung.com>
Reviewed-By: Giulio Camuffo <65adf162ac3b23aefeb12d72b964c762bc76d738@gmail.com>
Reviewed-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>

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