meson: drop indent level from xwayland

Use the pattern to avoid identing everything, when everything in the
file is under the one conditional.

Helps readability.

Signed-off-by: Pekka Paalanen <pq@iki.fi>

xwayland/meson.build

@@ -1,4 +1,7 @@
-if get_option('xwayland')
+if not get_option('xwayland')
+	subdir_done()
+endif
+
 srcs_xwayland = [
 	'launcher.c',
 	'window-manager.c',
@@ -28,4 +31,3 @@ if get_option('xwayland')
 env_modmap += 'xwayland.so=@0@;'.format(plugin_xwayland.full_path())
 
 install_headers('xwayland-api.h', subdir: dir_include_libweston)
-endif