Add -Wno-unused-function

This is temporary, it helps while we work on porting and large swaths of
the code are commented out.

meson.build

@@ -10,6 +10,7 @@ project(
 )
 
 add_project_arguments('-Wno-unused-parameter', language: 'c')
+add_project_arguments('-Wno-unused-function', language: 'c')
 
 cc = meson.get_compiler('c')