Fix #77794: Incorrect Date header format in built-in server

- Fix the date format to be compliant with https://tools.ietf.org/html/rfc7231#section-7.1.1.2
- Fix date format length and use GMT time
- Previously, local time was used instead of GMT.
- Remove extra whitespace
- Simplify string appends in php_cli_server.c

Author: kelunik

sapi/cli/php_cli_server.c

@@ -349,17 +349,16 @@ static void append_essential_headers(smart_str* buffer, php_cli_server_client *c
 	struct timeval tv = {0};
 
 	if (NULL != (val = zend_hash_str_find_ptr(&client->request.headers, "host", sizeof("host")-1))) {
-		smart_str_appendl_ex(buffer, "Host", sizeof("Host") - 1, persistent);
-		smart_str_appendl_ex(buffer, ": ", sizeof(": ") - 1, persistent);
+		smart_str_appends_ex(buffer, "Host: ", persistent);
 		smart_str_appends_ex(buffer, val, persistent);
-		smart_str_appendl_ex(buffer, "\r\n", 2, persistent);
+		smart_str_appends_ex(buffer, "\r\n", persistent);
 	}
 
 	if (!gettimeofday(&tv, NULL)) {
-		zend_string *dt = php_format_date("r", 1, tv.tv_sec, 1);
-		smart_str_appendl_ex(buffer, "Date: ", 6, persistent);
+		zend_string *dt = php_format_date("D, d M Y H:i:s", sizeof("D, d M Y H:i:s") - 1, tv.tv_sec, 0);
+		smart_str_appends_ex(buffer, "Date: ", persistent);
 		smart_str_appends_ex(buffer, dt->val, persistent);
-		smart_str_appendl_ex(buffer, "\r\n", 2, persistent);
+		smart_str_appends_ex(buffer, " GMT\r\n", persistent);
 		zend_string_release(dt);
 	}