To make the PostgreSQL server packages build reproducibly, we need to remove
the build path from -fdebug-prefix-map and -ffile-prefix-map in CFLAGS.

* The actual server build still uses the original CFLAGS so the build path is
  correctly mapped in the object files.
* The information printed by the pg_config binary and the system view is
  filtered in src/common/Makefile and the configure script.
* The build paths stored in Makefile.global are filtered in debian/rules.
  (abs_top_builddir, abs_top_srcdir, configure_args, CFLAGS)
* To make PGXS module builds reproducible, pg_buildext copies the environment
  CFLAGS to COPT where Makefile.global picks them up, using the prefix maps
  from dpkg-buildflags.

--- a/src/common/Makefile
+++ b/src/common/Makefile
@@ -33,7 +33,7 @@ STD_CPPFLAGS := $(filter-out -I$(top_src
 STD_LDFLAGS := $(filter-out -L$(top_builddir)/src/common -L$(top_builddir)/src/port,$(LDFLAGS))
 override CPPFLAGS += -DVAL_CC="\"$(CC)\""
 override CPPFLAGS += -DVAL_CPPFLAGS="\"$(STD_CPPFLAGS)\""
-override CPPFLAGS += -DVAL_CFLAGS="\"$(CFLAGS)\""
+override CPPFLAGS += -DVAL_CFLAGS="\"$(filter-out -fdebug-prefix-map=% -ffile-prefix-map=%,$(CFLAGS))\""
 override CPPFLAGS += -DVAL_CFLAGS_SL="\"$(CFLAGS_SL)\""
 override CPPFLAGS += -DVAL_LDFLAGS="\"$(STD_LDFLAGS)\""
 override CPPFLAGS += -DVAL_LDFLAGS_EX="\"$(LDFLAGS_EX)\""
--- a/configure.in
+++ b/configure.in
@@ -27,6 +27,7 @@ AC_COPYRIGHT([Copyright (c) 1996-2020, P
 AC_CONFIG_SRCDIR([src/backend/access/common/heaptuple.c])
 AC_CONFIG_AUX_DIR(config)
 AC_PREFIX_DEFAULT(/usr/local/pgsql)
+[ac_configure_args=$(echo "$ac_configure_args" | sed -e "s/ -f\(debug\|file\)-prefix-map=[^' ]*//g")]
 AC_DEFINE_UNQUOTED(CONFIGURE_ARGS, ["$ac_configure_args"], [Saved arguments from configure])
 
 [PG_MAJORVERSION=`expr "$PACKAGE_VERSION" : '\([0-9][0-9]*\)'`]
--- a/configure
+++ b/configure
@@ -2796,6 +2796,7 @@ ac_config_sub="$SHELL $ac_aux_dir/config
 ac_configure="$SHELL $ac_aux_dir/configure"  # Please don't use this var.
 
 
+ac_configure_args=$(echo "$ac_configure_args" | sed -e "s/ -f\(debug\|file\)-prefix-map=[^' ]*//g")
 
 
 cat >>confdefs.h <<_ACEOF