[gdb, hurd] Adjust to Hurd "proc" interface changes

[gdb, hurd] Adjust to Hurd "proc" interface changes

Hurd's commit baf7e5c8ce176aead15c2559952d8bdf0da41ffd "hurd: Use polymorphic
port types to return some rights" causes in the GDB build:

    /usr/bin/ld: process_reply_S.o: in function `_Xproc_pid2proc_reply':
    [...]/gdb/process_reply_S.c:754: undefined reference to `S_proc_pid2proc_reply'
    /usr/bin/ld: [...]/gdb/process_reply_S.c:730: undefined reference to `S_proc_pid2proc_reply'
    /usr/bin/ld: process_reply_S.o: in function `_Xproc_task2proc_reply':
    [...]/gdb/process_reply_S.c:589: undefined reference to `S_proc_task2proc_reply'
    /usr/bin/ld: [...]/gdb/process_reply_S.c:565: undefined reference to `S_proc_task2proc_reply'
    /usr/bin/ld: process_reply_S.o: in function `_Xproc_getmsgport_reply':
    [...]/gdb/process_reply_S.c:204: undefined reference to `S_proc_getmsgport_reply'
    /usr/bin/ld: [...]/gdb/process_reply_S.c:180: undefined reference to `S_proc_getmsgport_reply'
    collect2: error: ld returned 1 exit status

	gdb/
	* gnu-nat.c (S_proc_getmsgport_reply, S_proc_task2proc_reply)
	(S_proc_pid2proc_reply): Adjust to Hurd "proc" interface changes.