PHP2Shell on PHP 7: patch applied is not patch compiled is not patch working

The official 7.4 backport is one commit, 17 files, +240/-59. For 7.1 to 7.3 the sury patch sets need a prerequisite that patch --dry-run cannot see: ZSTR_MAX_LEN, which the fix references 38 times and which is absent from every vanilla PHP 7.3 and older. Three layers of verification, and the one static marker that works on 7.x.