New header varatt.h split off from postgres.h

This new header contains all the variable-length data types support
(TOAST support) from postgres.h, which isn't needed by large parts of
the backend code.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/ddcce239-0f29-6e62-4b47-1f8ca742addf%40enterprisedb.com

src/backend/utils/adt/network_spgist.c

@@ -37,6 +37,7 @@
 #include "catalog/pg_type.h"
 #include "utils/builtins.h"
 #include "utils/inet.h"
+#include "varatt.h"
 
 
 static int	inet_spg_node_number(const inet *val, int commonbits);