This is not enabled by -Wextra and seems like something sane to have which is not much effort to make work.

Except for this one:

In file included from Zend/zend_language_scanner.l:38:0:
Zend/zend_language_parser.h:38:5: warning: "YYDEBUG" is not defined [-Wundef]
 #if YYDEBUG
     ^

Which is generated by Bison but I also don't understand why the compilers are complaining as the generated code is (at least locally):

/* Debug traces.  */
#ifndef ZENDDEBUG
# if defined YYDEBUG
#if YYDEBUG
#   define ZENDDEBUG 1
#  else
#   define ZENDDEBUG 0
#  endif
# else /* ! defined YYDEBUG */
#  define ZENDDEBUG 0
# endif /* ! defined YYDEBUG */
#endif  /* ! defined ZENDDEBUG */

Note, I realized that the following macros are always defined, but only on Windows:

AC_DEFINE('HAVE_GAI_STRERROR', main_network_has_ipv6);
AC_DEFINE('HAVE_IPV6', main_network_has_ipv6);

Fixed with: ca6dd7e

AC_DEFINE('HAVE_GETADDRINFO', main_network_has_ipv6);
See https://heap.space/xref/php-src/win32/build/config.w32?r=84854a72#283

Review list:

• Extensions:
  • BCMath
  • BZ2
  • Calendar
  • COM_DotNet
  • CType
  • cURL
  • Date
  • DBA
  • Dom
  • Enchant: about HAVE_ENCHANT_BROKER_SET_PARAM or need to always be defined for Nux* or need to drop always defined on Windows and adjust #if/#ifdef accordingly
  • EXIF
  • FFI - does #if FFI_CLOSURES need to be #ifdef FFI_CLOSURES?
  • Fileinfo
  • Filter
  • FTP
  • GD
  • GetText
  • GMP
  • Hash
  • Iconv
  • IMAP
  • INTL
  • JSON
  • LDAP
  • LibXML
  • MBString
  • MySQLi
  • MySQLnd
  • OCI8 - currently bundling with #5603
  • ODBC
  • OpCache - Needs to be reviewed
  • OpenSSL
  • PCNTL
  • PCRE
  • PDO
  • PDO_DBLIB
  • PDO_FIREBIRD
  • PDO_MYSQL
  • PDO_OCI
  • PDO_ODBC
  • PDO_PGSQL
  • PDO_SQLite
  • PGSQL
  • PHAR
  • POSIX
  • PSpell
  • Readline
  • Reflection
  • Session
  • SHMOP
  • SimpleXML
  • Skeleton
  • SNMP - Need to resolve HAVE_GETADDRINFO issue before finished
  • Soap
  • Sockets - Need to resolve HAVE_GETADDRINFO issue before finished
  • Sodium
  • SPL
  • SQLite3
  • Standard:
    • base64
  • Sysvmsg
  • Sysvsem
  • Sysvshm
  • Tidy
  • Tokenizer
  • XML
  • XMLReader
  • XMLRPC Ignoring this as it's getting unbundled
  • XMLWriter
  • XSL
  • zend_test
  • ZIP
  • ZLib
• main/
• SAPIs:
  • Apache2Handler
  • CGI
  • CLI (may want to reconfirm)
  • Embed
  • FPM (may want to reconfirm)
  • Fuzzer
  • LiteSpeed
  • PHPDBG (may want to reconfirm)
• TSRM
• Win32
• Zend/