pg_upgrade: Avoid check target accidentally breaking make's --output-sync.
pg_upgrade: Avoid check target accidentally breaking make's --output-sync.

When $(MAKE) is present in a rule, make assumes that target is a
submake, and it doesn't need to buffer its output. But in this case
it's a shell script that needs buffered output. Avoid that heuristic,
by referring to $(MAKE) via an indirection.

Discussion: f3b805f1346618bf822c9861d94f2b1ff7bf386d@alap3.anarazel.de

xinzweb/gpdb,adam8157/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,adam8157/gpdb,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,50wu/gpdb,adam8157/gpdb,lisakowen/gpdb,adam8157/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,adam8157/gpdb,50wu/gpdb,adam8157/gpdb,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,greenplum-db/gpdb