strengthen check for --forkchild in main()

    Attachment (forkchild_check.patch) at 2024-06-17 18:36:00 from Nathan Bossart <nathandbossart at gmail.com> (Patch: Yes)
    Attachment (v1-0001-Add-child_process_kinds-static-assert.patch) at 2024-03-21 10:31:17 from Jelte Fennema-Nio <postgres at jeltef.nl> (Patch: Yes)
    Attachment (v13-0001-Improve-log-messages-referring-to-background-wor.patch) at 2024-03-13 07:30:27 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v12-0001-Pass-CAC-as-argument-to-backend-process.patch) at 2024-03-04 09:05:08 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v11-0001-Redefine-backend-ID-to-be-an-index-into-the-proc.patch) at 2024-02-22 00:37:16 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v10-0001-Remove-superfluous-pgprocno-field-from-PGPROC.patch) at 2024-02-08 11:19:53 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v9-0001-Remove-superfluous-pgprocno-field-from-PGPROC.patch) at 2024-02-01 13:54:23 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v8-0001-Remove-superfluous-pgprocno-field-from-PGPROC.patch) at 2024-01-30 00:08:36 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v7-0001-Remove-superfluous-pgprocno-field-from-PGPROC.patch) at 2024-01-24 23:51:02 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v6-0001-Fix-incorrect-comment-on-how-BackendStatusArray-i.patch) at 2024-01-10 12:35:52 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v5-0001-Pass-CAC-as-argument-to-backend-process.patch) at 2023-12-08 12:33:33 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v4-0001-Refactor-CreateSharedMemoryAndSemaphores.patch) at 2023-12-01 12:10:03 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v3-0001-Refactor-CreateSharedMemoryAndSemaphores.patch) at 2023-11-29 23:36:25 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v2-0001-Pass-background-worker-entry-in-the-parameter-fil.patch) at 2023-10-11 11:12:47 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (0001-Refactor-ListenSocket-array.patch) at 2023-08-29 06:58:48 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (fix-syslogger-closesocket-errors.patch) at 2023-08-28 20:52:15 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (v2-0001-Use-FD_CLOEXEC-on-ListenSockets.patch) at 2023-08-24 11:41:44 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)
    Attachment (0001-Allocate-Backend-structs-in-PostmasterContext.patch) at 2023-06-18 11:22:33 from Heikki Linnakangas <hlinnaka at iki.fi> (Patch: Yes)