GDB: Add set/show serial parity command.

GDB: Add set/show serial parity command.

The "set serial parity" command allows the user to control which
parity to use when communicating over a serial connection, rather
than having the parity hardcoded to none.

gdb/ChangeLog:

        * NEWS: Mention set/show serial parity command.
        * monitor.c (monitor_open): Call serial_setparity.
        * remote.c (remote_open_1): Likewise.
        * ser-base.c (ser_base_serparity): New function.
        * ser-base.h (ser_base_setparity): Add  declaration.
        * ser-go32.c (dos_ops): Set "setparity" field.
        * ser-mingw.c (ser_windows_raw): Do not set state.fParity and
        state.Parity.
        (ser_windows_setparity): New function.
        (hardwire_ops): Add ser_windows_setparity.
        (tty_ops): Add NULL for setparity field.
        (pipe_ops): Add ser_base_setparity.
        (tcp_ops): Likewise.
        * ser-pipe.c (pipe_ops): Likewise.
        * ser-tcp.c (tcp_ops): Likewise.
        * ser-unix.c (hardwire_setparity): Add declaration.
        (hardwire_raw): Don't reset PARENB flag.
        (hardwire_setparity): New function.
        (hardwire_ops): Add hardwire_setparity.
        * serial.c (serial_setparity): New function.
        (serial_parity): New global.
        (parity_none, parity_odd, parity_even, parity_enums, parity):
        New static globals.
        (set_parity): New function.
        (_initialize_serial): Add set/show serial parity commands.
        * serial.h (GDBPARITY_NONE): Define.
        (GDBPARITY_ODD): Define.
        (GDBPARITY_EVEN): Define.
        (serial_setparity) Add declaration.
        (struct serial_ops): Add setparity field.
        * target.h (serial_parity): Add declaration.

gdb/doc/ChangeLog:

        * gdb.texinfo (Remote configuration): Document "set/show
        serial parity" command.