Commit bad51a49 tried to use a shortcut with just one stamp file
recording the actions of generating the pg_*_d.h headers and copying
them to the src/include/catalog/ directory.  That doesn't work in all
scenarios though, so we must use two stamp files like the Makefiles do.

John Naylor

Discussion: https://postgr.es/m/CANFyU944GdHr=puPbA78STnqr=8kgMrGF-VDHck6aO_-qNDALg@mail.gmail.com