Starting with ORCA version 2.2, there's a gpos/config.h file that contains
flags describing the compile-time options used to build the ORCA library.
Those flags affect binary compatibility, so it's important that e.g. if
ORCA was built with GPOS_DEBUG, the code that uses it (src/backend/gpopt
in this case) is also built with GPOS_DEBUG. Use the new gpos/config.h
for that, instead of deriving them ourselves and hoping that we reach the
same conclusions as whoever built ORCA.

This requires ORCA v2.2, so update releng.mk to download that.