[HURD] Improve the GDB Port for GNU Hurd

by hacklu for GNU Project

Many cases show that the GDB on GNU Hurd is not so good as on GNU/Linux in terms of functionality and integrity. The former eagerly need to improve the porting such as fixing the bug and make up the defect of missing important component like gdbserver. Gdbserver makes it possible to remotely debug. Without the porting of gdbserver, the porting of GDB to GNU Hurd is incomplete.