Always use lib/girepository-1.0 as gir typelib install dir.

modules/gnome.py

@@ -73,7 +73,9 @@ class GnomeModule:
         typelib_cmd = ['g-ir-compiler', scan_target, '--output', '@OUTPUT@']
         kwargs['output'] = typelib_output
         kwargs['command'] = typelib_cmd
-        kwargs['install_dir'] = os.path.join(state.environment.get_libdir(), 'girepository-1.0')
+        # Note that this can't be libdir, because e.g. on Debian it points to
+        # lib/x86_64-linux-gnu but the girepo dir is always under lib.
+        kwargs['install_dir'] = 'lib/girepository-1.0'
         typelib_target = TypelibTarget(typelib_name, state.subdir, kwargs)
         return [scan_target, typelib_target]