gdb_main: Modify qC (current thread id) and qfThreadInfo to report multiprocess p1.1 thread name

* This change should match p1.1 in halt-responses, without "QCp1.1" GDB-15 breaks after vKill/vRun.
> In addition, the remote protocol supports a multiprocess feature
  in which the thread-id syntax is extended to optionally include
  both process and thread ID fields, as ‘ppid.tid’.

Author: ALTracer

src/gdb_main.c

@@ -571,7 +571,7 @@ static void exec_q_c(const char *packet, const size_t length)
 {
 	(void)packet;
 	(void)length;
-	gdb_put_packet_str("QC1");
+	gdb_put_packet_str("QCp1.1");
 }
 
 /*
@@ -585,7 +585,7 @@ static void exec_q_thread_info(const char *packet, const size_t length)
 {
 	(void)length;
 	if (packet[-11] == 'f' && cur_target)
-		gdb_put_packet_str("m1");
+		gdb_put_packet_str("mp1.1");
 	else
 		gdb_put_packet_str("l");
 }