gobject: Ensure gobject from builddir is used when generating GLib-2.0.gir

Otherwise the installed one will be used, which will mean that new API
will not be available when linking.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

gobject/meson.build

@@ -190,6 +190,7 @@ if enable_gir
       '-DGLIB_COMPILATION',
       '-DGETTEXT_PACKAGE="dummy"',
       '--symbol-prefix=glib',
+      '--library-path=' + meson.current_build_dir(),
       '--library=gobject-2.0',
     ],
   )