[#25477] YSQL: disable check_pghost_envvar

Summary:
`check_pghost_envvar` is used by Postgres to validate that the pg server we are connecting to for upgrade to is a local server. It checks for conditions:
```
(strcmp(value, "localhost") != 0 && strcmp(value, "127.0.0.1") != 0 && strcmp(value, "::1") != 0 && !is_unixsock_path(value)))
```

However, in Yugabyte, the servers don't necessarily match this layout. `test_upgrade.sh` creates a server with IP 127.0.0.200, which causes `check_pghost_envvar` to fail with
```
+ build/latest/postgres/bin/pg_upgrade --old-datadir /tmp/pg15_cluster_data/node-1/disk-1/pg_data --old-host 127.0.0.200 --old-port 5433 --username yugabyte --check

libpq environment variable PGHOST has a non-local server value: 127.0.0.200
```

Rather than updating this check to work for every possible scenario in Yugabyte, it is simpler to just disable the check for Yugabyte, since the new cluster creation is owned by Yugabyte anyways.
Jira: DB-14727

Test Plan:
Jenkins
```
pg15_tests/test_upgrade.sh
```

Reviewers: hsunder, fizaa

Reviewed By: hsunder

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D41041

src/postgres/src/bin/pg_upgrade/option.c

@@ -23,6 +23,9 @@ static void check_required_directory(char **dirpath,
 									 const char *envVarName, bool useCwd,
 									 const char *cmdLineOption, const char *description,
 									 bool missingOk);
+
+static void yb_check_sockdir(ClusterInfo *cluster);
+
 #define FIX_DEFAULT_READ_ONLY "-c default_transaction_read_only=false"
 
 
@@ -274,6 +277,9 @@ parseCommandLine(int argc, char *argv[])
 	check_required_directory(&user_opts.socketdir, "PGSOCKETDIR", true,
 							 "-s", _("sockets will be created"), false);
 
+	if (is_yugabyte_enabled() && !user_opts.check)
+		yb_check_sockdir(&new_cluster);
+
 #ifdef WIN32
 
 	/*
@@ -541,3 +547,12 @@ get_sock_dir(ClusterInfo *cluster, bool live_check)
 	cluster->sockdir = NULL;
 #endif
 }
+
+static void
+yb_check_sockdir(ClusterInfo *cluster)
+{
+	Assert(is_yugabyte_enabled());
+
+	if (!cluster->sockdir)
+		pg_fatal("socket directory must be specified\n");
+}

src/postgres/src/bin/pg_upgrade/pg_upgrade.c

@@ -361,10 +361,12 @@ setup(char *argv0, bool *live_check)
 	 * make sure the user has a clean environment, otherwise, we may confuse
 	 * libpq when we connect to one (or both) of the servers.
 	 */
-#ifdef YB_TODO
-	/* Investigate/implement this check */
-	check_pghost_envvar();
-#endif
+	if (!is_yugabyte_enabled())
+		/*
+		 * YB: New cluster creation is controlled by Yugabyte, but the IP
+		 * addresses don't match the expected values of this check.
+		 */
+		check_pghost_envvar();
 
 	/*
 	 * In case the user hasn't specified the directory for the new binaries