Fix GH-12999: zend_strnlen build fix when platform misses strnlen support.

fix from @rainerjung

Author: devnexen

Diff for: NEWS

@@ -5,6 +5,7 @@ PHP                                                                        NEWS
 - Core:
   . Fixed bug GH-12953 (false positive SSA integrity verification failed when
     loading composer classmaps with more than 11k elements). (nielsdos)
+  . Fixed bug GH-12999 (zend_strnlen build when strnlen is unsupported). (rainerjung)
 
 - Cli:
   . Fix incorrect timeout in built-in web server when using router script and

Diff for: Zend/zend_operators.h

@@ -269,7 +269,7 @@ static zend_always_inline size_t zend_strnlen(const char* s, size_t maxlen)
 #if defined(HAVE_STRNLEN)
 	return strnlen(s, maxlen);
 #else
-	const char *p = memchr(s, '\0', maxlen);
+	const char *p = (const char *)memchr(s, '\0', maxlen);
 	return p ? p-s : maxlen;
 #endif
 }