migration: Teach it about G_SOURCE_REMOVE

As this is defined on glib 2.32, add compatibility macros for older glibs.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
diff --git a/include/glib-compat.h b/include/glib-compat.h
index fcffcd3..e15aca2 100644
--- a/include/glib-compat.h
+++ b/include/glib-compat.h
@@ -223,6 +223,8 @@
 {
     return g_hash_table_lookup_extended(hash_table, key, NULL, NULL);
 }
+#define G_SOURCE_CONTINUE TRUE
+#define G_SOURCE_REMOVE FALSE
 #endif
 
 #ifndef g_assert_true