[php-src] Issue #8397: crypt() accepts invalid characters in salt

Issue: https://github.com/php/php-src/issues/8397 Comment Author: nikic As to the original issue, I'm not sure there's much we can do here -- the validation here is clearly a moving target for the system implementation, so if we adopted the stricter validation seen on Ubuntu 20.04 we would not fail to process hashes from Ubuntu 18.04. I think the only viable option here is to recommend users who care about interoperability with system crypt to build with --with-external-libcrypt, in which case we'd want to reclassify this as a documentation issue.