allow for more graceful migration - don't err on now ignored X modifier

Author: SjonHortensius

UPGRADING

@@ -147,8 +147,8 @@ PHP 8.0 UPGRADE NOTES
 
 - PCRE:
   . When passing invalid escape sequences they are no longer intepreted as
-    literals. This behaviour previously required the X modifier - which has
-    been removed as well.
+    literals. This behaviour previously required the X modifier - which is
+    now ignored.
 
 - PDO:
   . The method PDOStatement::setFetchMode() now accepts the following signature:

ext/pcre/php_pcre.c

@@ -694,6 +694,7 @@ PHPAPI pcre_cache_entry* pcre_get_compiled_regex_cache(zend_string *regex)
 			case 'A':	coptions |= PCRE2_ANCHORED;		break;
 			case 'D':	coptions |= PCRE2_DOLLAR_ENDONLY;break;
 			case 'S':	/* Pass. */					break;
+			case 'X':	/* Pass. */					break;
 			case 'U':	coptions |= PCRE2_UNGREEDY;		break;
 			case 'u':	coptions |= PCRE2_UTF;
 	/* In  PCRE,  by  default, \d, \D, \s, \S, \w, and \W recognize only ASCII

ext/pcre/tests/pcre_extra.phpt

@@ -1,5 +1,5 @@
 --TEST--
-X (PCRE_EXTRA) modififier is no longer functional
+X (PCRE_EXTRA) modififier is ignored (no error, no change)
 --FILE--
 <?php
 
@@ -11,5 +11,5 @@ var_dump(preg_match('/\y/X', '\y'));
 Warning: preg_match(): Compilation failed: unrecognized character follows \ at offset 1 in %spcre_extra.php on line 3
 bool(false)
 
-Warning: preg_match(): Unknown modifier 'X' in %spcre_extra.php on line 4
+Warning: preg_match(): Compilation failed: unrecognized character follows \ at offset 1 in %spcre_extra.php on line 4
 bool(false)