We don't build/install interfaces by upstream's implicit rules.

This patch is used on two places; postgresql.spec and libecpg.spec -- keep those

in sync!

Related: rhbz#1618698

diff -ur postgresql-12.2/src/Makefile postgresql-12.2_patch/src/Makefile

--- postgresql-12.2/src/Makefile	2020-02-10 23:14:51.000000000 +0100

+++ postgresql-12.2_patch/src/Makefile	2020-03-02 12:49:45.530666894 +0100

@@ -20,7 +20,6 @@

 	backend/utils/mb/conversion_procs \

 	backend/snowball \

 	include \

-	interfaces \

 	backend/replication/libpqwalreceiver \

 	backend/replication/pgoutput \

 	fe_utils \

diff -ur postgresql-12.2/src/Makefile.global.in postgresql-12.2_patch/src/Makefile.global.in

--- postgresql-12.2/src/Makefile.global.in	2020-02-10 23:14:51.000000000 +0100

+++ postgresql-12.2_patch/src/Makefile.global.in	2020-03-02 12:47:40.970583609 +0100

@@ -550,7 +550,7 @@

 # How to link to libpq.  (This macro may be used as-is by backend extensions.

 # Client-side code should go through libpq_pgport or libpq_pgport_shlib,

 # instead.)

-libpq = -L$(libpq_builddir) -lpq

+libpq = -lpq

 # libpq_pgport is for use by client executables (not libraries) that use libpq.

 # We force clients to pull symbols from the non-shared libraries libpgport

@@ -580,7 +580,6 @@

 # Commonly used submake targets

 submake-libpq: | submake-generated-headers

-	$(MAKE) -C $(libpq_builddir) all

 submake-libpgport: | submake-generated-headers

 	$(MAKE) -C $(top_builddir)/src/port all