automake: Don't fail the build if we can't setuid.

The configure default is to setuid root the weston compositor.
However, if installing as non-root (say, to your prefix in homedir),
the install fails anyway, even if you didn't need setuid to run weston
in your configuration.

src/Makefile.am

@@ -26,8 +26,8 @@ weston_SOURCES =			\
 
 if ENABLE_SETUID_INSTALL
 install-exec-hook:
-	chown root $(DESTDIR)$(bindir)/weston
+	-chown root $(DESTDIR)$(bindir)/weston
-	chmod u+s $(DESTDIR)$(bindir)/weston
+	-chmod u+s $(DESTDIR)$(bindir)/weston
 endif
 
 if ENABLE_XSERVER_LAUNCHER