meson: Do not list Clapper API features when not building it

No need to list API features if API is not being built.

This avoids an issue with meson script error when Clapper API
build is skipped, since these are not declared then.

Fixes #468

meson.build

@@ -146,6 +146,8 @@ summary('introspection', build_gir ? 'Yes' : 'No', section: 'Build')
 summary('vapi', build_vapi ? 'Yes' : 'No', section: 'Build')
 summary('doc', build_doc  ? 'Yes' : 'No', section: 'Build')
 
-foreach name : clapper_possible_features
-  summary(name, clapper_available_features.contains(name) ? 'Yes' : 'No', section: 'Features')
-endforeach
+if build_clapper
+  foreach name : clapper_possible_features
+    summary(name, clapper_available_features.contains(name) ? 'Yes' : 'No', section: 'Features')
+  endforeach
+endif