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 <derekf@osg.samsung.com>
Reviewed-By: Giulio Camuffo <giuliocamuffo@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

Makefile.am

@@ -165,7 +165,7 @@ install-exec-hook:
 	chown root $(DESTDIR)$(bindir)/weston-launch \
 		&& chmod u+s $(DESTDIR)$(bindir)/weston-launch \
 		&& can_suid_files=yes;\
-	if test $$can_suid_files=no; then \
+	if test $$can_suid_files = no; then \
 		echo 'Error: unable to unable to change ownership/setuid on weston-launch.'; \
 		echo 'To skip this step, re-run ./configure using --disable-setuid-install'; \
 		false; \