fix gcc compilation

Author: ochafik

common/chat-parser.cpp

@@ -88,6 +88,7 @@ void common_chat_msg_parser::finish() {
     }
 }
 
+[[noreturn]] 
 void common_chat_msg_parser::incomplete(const std::string & message) {
     if (is_partial_) {
         finish();

common/chat-parser.h

@@ -63,6 +63,7 @@ class common_chat_msg_parser {
 
     void finish();
 
+    [[noreturn]] 
     void incomplete(const std::string & message);
 
     bool consume_spaces();

common/regex-partial.cpp

@@ -1,6 +1,7 @@
 #include "regex-partial.h"
 #include "common.h"
 #include <functional>
+#include <optional>
 
 common_regex::common_regex(const std::string & pattern) :
     pattern(pattern),