[ticket/9574] Add pcre_utf8_support() function

Refactor the check for PCRE UTF-8 support into a new pcre_utf8_support()
function.

PHPBB3-9574

phpBB/includes/functions.php

@@ -4507,3 +4507,19 @@ function phpbb_user_session_handler()
 
 	return;
 }
+
+/**
+* Check if PCRE has UTF-8 support
+* PHP may not be linked with the bundled PCRE lib and instead with an older version
+*
+* @return bool	Returns true if PCRE (the regular expressions library) supports UTF-8 encoding
+*/
+function pcre_utf8_support()
+{
+	static $utf8_pcre_properties = null;
+	if (is_null($utf8_pcre_properties))
+	{
+		$utf8_pcre_properties = (@preg_match('/\p{L}/u', 'a') !== false);
+	}
+	return $utf8_pcre_properties;
+}