ntdll: Adds support for custom serial port baudrates on Mac

[Nikolay Sivov]

On 11/29/2014 07:53 PM, Nathan Fearnley wrote:
> Mac OS X supports a special function call for custom baud rates. I have
> implemented this feature to allow non-standard baud rates.
> Unfortunately, setting any other parameters using tcsetattr will fail,
> because it does not support the higher baud rates. In order to work
> around this, when setting other parameters, the baud rate is temporarily
> set to 9600, then reset back to custom rate after the changes are complete.
>
>

I can't comment on functional part, but regarding code structure this 
should be better separated imho. Maybe it's even better to duplicate 
whole functions and ifdef them all in case when __APPLE__ is not 
defined. Also don't use C++ 'bool', use BOOL with TRUE/FALSE defines.