Supress warnings from C code generated from Vala example

Author: wmww

examples/meson.build

@@ -20,5 +20,6 @@ if get_option('vapi')
         'simple-example-vala',
         files('simple-example.vala'),
         dependencies: [gtk, gtk_layer_shell, vapi],
+        c_args: ['-Wno-unused-but-set-variable', '-Wno-unused-parameter', '-Wno-cast-function-type'],
         install: false)
 endif