Another updated version attached -- fix missing manifest version check in pg_verifybackup before system identifier validation.
Thinking a bit more on this, I realized parse_manifest_file() has many out parameters. Instead parse_manifest_file() should simply return manifest data like load_backup_manifest(). Attached 0001 patch doing the same, and removed parser_context structure, and added manifest_data, and did the required adjustments to pg_verifybackup code.