Add PG_TEST_EXTRA configure option to the Make builds

The Meson builds have PG_TEST_EXTRA as a configure-time variable,
which was not available in the Make builds. To ensure both build
systems are in sync, PG_TEST_EXTRA is now added as a configure-time
variable. It can be set like this:

    ./configure PG_TEST_EXTRA="kerberos, ssl, ..."

Note that to preserve the old behavior, this configure-time variable
is overridden by the PG_TEST_EXTRA environment variable when you run
the tests.

Author: Jacob Champion
Reviewed by: Ashutosh Bapat, Nazir Bilal Yavuz

src/Makefile.global.in

@@ -642,6 +642,16 @@ submake-libpgfeutils: | submake-generated-headers
 #
 # Testing support
 
+# Store any configure-time setting for PG_TEST_EXTRA, but let environment
+# variables override it to maintain the historical behavior of the tests.
+# (Standard `=` assignment would require devs to use a commandline option.)
+# This is skipped in PGXS mode to keep the setting from escaping into other
+# projects' builds.
+ifndef PGXS
+PG_TEST_EXTRA ?= @PG_TEST_EXTRA@
+export PG_TEST_EXTRA
+endif
+
 ifneq ($(USE_MODULE_DB),)
   PL_TESTDB = pl_regression_$(NAME)
   ifneq ($(MODULE_big),)

src/test/Makefile

@@ -27,11 +27,6 @@ ifeq ($(with_ssl),openssl)
 SUBDIRS += ssl
 endif
 
-# Test suites that are not safe by default but can be run if selected
-# by the user via the whitespace-separated list in variable PG_TEST_EXTRA.
-# Export PG_TEST_EXTRA to check it in individual tap tests.
-export PG_TEST_EXTRA
-
 # We don't build or execute these by default, but we do want "make
 # clean" etc to recurse into them.  (We must filter out those that we
 # have conditionally included into SUBDIRS above, else there will be