Add G_SOURCE_REMOVE to vir-glib-compat

G_SOURCE_REMOVE was introduced in GLib 2.32 and has its value defined as
FALSE.

src/virt-glib-compat.h

@@ -71,6 +71,11 @@ G_BEGIN_DECLS
 GByteArray *g_byte_array_new_take (guint8 *data, gsize len);
 #endif
 
+#if !GLIB_CHECK_VERSION(2,32,0)
+#define G_SOURCE_CONTINUE   TRUE
+#define G_SOURCE_REMOVE     FALSE
+#endif
+
 G_END_DECLS
 
 #endif // _VIRT_GLIB_COMPAT_H