Merge dblink's paths test script into its main test.

There's no longer any reason to fire up a separate psql run
to create these functions.  (Some refactoring in the main
regression tests is also called for, but that will take
more thought.)

Discussion: https://postgr.es/m/1655733.1639871614@sss.pgh.pa.us

Author: tglsfdc

contrib/dblink/Makefile

@@ -11,7 +11,7 @@ EXTENSION = dblink
 DATA = dblink--1.2.sql dblink--1.1--1.2.sql dblink--1.0--1.1.sql
 PGFILEDESC = "dblink - connect to other PostgreSQL databases"
 
-REGRESS = paths dblink
+REGRESS = dblink
 REGRESS_OPTS = --dlpath=$(top_builddir)/src/test/regress
 
 ifdef USE_PGXS

contrib/dblink/expected/dblink.out

@@ -1,4 +1,22 @@
 CREATE EXTENSION dblink;
+-- directory paths and dlsuffix are passed to us in environment variables
+\getenv abs_srcdir PG_ABS_SRCDIR
+\getenv libdir PG_LIBDIR
+\getenv dlsuffix PG_DLSUFFIX
+\set regresslib :libdir '/regress' :dlsuffix
+-- create some functions needed for tests
+CREATE FUNCTION setenv(text, text)
+   RETURNS void
+   AS :'regresslib', 'regress_setenv'
+   LANGUAGE C STRICT;
+CREATE FUNCTION wait_pid(int)
+   RETURNS void
+   AS :'regresslib'
+   LANGUAGE C STRICT;
+\set path :abs_srcdir '/'
+\set fnbody 'SELECT setenv(''PGSERVICEFILE'', ' :'path' ' || $1)'
+CREATE FUNCTION set_pgservicefile(text) RETURNS void LANGUAGE SQL
+    AS :'fnbody';
 -- want context for notices
 \set SHOW_CONTEXT always
 CREATE TABLE foo(f1 int, f2 text, f3 text[], primary key (f1,f2));

contrib/dblink/expected/paths.out

@@ -1,5 +1,28 @@
 CREATE EXTENSION dblink;
 
+-- directory paths and dlsuffix are passed to us in environment variables
+\getenv abs_srcdir PG_ABS_SRCDIR
+\getenv libdir PG_LIBDIR
+\getenv dlsuffix PG_DLSUFFIX
+
+\set regresslib :libdir '/regress' :dlsuffix
+
+-- create some functions needed for tests
+CREATE FUNCTION setenv(text, text)
+   RETURNS void
+   AS :'regresslib', 'regress_setenv'
+   LANGUAGE C STRICT;
+
+CREATE FUNCTION wait_pid(int)
+   RETURNS void
+   AS :'regresslib'
+   LANGUAGE C STRICT;
+
+\set path :abs_srcdir '/'
+\set fnbody 'SELECT setenv(''PGSERVICEFILE'', ' :'path' ' || $1)'
+CREATE FUNCTION set_pgservicefile(text) RETURNS void LANGUAGE SQL
+    AS :'fnbody';
+
 -- want context for notices
 \set SHOW_CONTEXT always