compile errors on 2.4.2-ac16

[Ken Hill]

serial.c: In function `wait_for_xmitr':
serial.c:5497: `ASYNC_NO_FLOW' undeclared (first use in this function)
serial.c:5497: (Each undeclared identifier is reported only once
serial.c:5497: for each function it appears in.)
serial.c: In function `serial_console_setup':
serial.c:5666: `ASYNC_NO_FLOW' undeclared (first use in this function)
make[3]: *** [serial.o] Error 1
make[3]: Leaving directory `/usr/src/linux/drivers/char'
make[2]: *** [first_rule] Error 2
make[2]: Leaving directory `/usr/src/linux/drivers/char'
make[1]: *** [_subdir_char] Error 2
make[1]: Leaving directory `/usr/src/linux/drivers'
make: *** [_dir_drivers] Error 2

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