Silence C warnings (#2734)

...and enable warnings about deprecated stuff from Vala

Author: lenemter

meson.build

@@ -36,7 +36,6 @@ glib_version_required = '2.78'
 add_project_arguments([
         '--target-glib=' + glib_version_required,
         '--hide-internal',
-        '--enable-deprecated',
         '--vapidir=' + vapi_dir,
     ],
     language: 'vala',
@@ -45,6 +44,9 @@ add_project_arguments([
         '-Wno-discarded-qualifiers',
         '-Wno-incompatible-pointer-types',
         '-Wno-unused',
+        '-Wno-address',
+        '-Wno-duplicate-decl-specifier',
+        '-Wno-deprecated-declarations',
         '-Wl,--enable-new-dtags',
 
         '-DGETTEXT_PACKAGE="@0@"'.format(meson.project_name()),

src/Background/BackgroundContainer.vala

@@ -26,6 +26,8 @@ public class Gala.BackgroundContainer : Meta.BackgroundGroup {
             if (event.get_button () == Clutter.Button.SECONDARY) {
                 show_background_menu ((int)x, (int)y);
             }
+
+            return Source.CONTINUE;
         });
 
 #if HAS_MUTTER47