Revise use of serial port comms related macros in Windows branch

[jimklimov]

Such definitions in drivers/serial.h may be not portable across versions of Windows and build toolkits, but apparently got the builds passing at this time.

At some point probably we should detect in configure if they are needed in the first place (or use more #ifndef clauses at least):

/* porting stuff for WIN32 */
#ifdef WIN32
/* TODO : support "open" flags */
# define O_NONBLOCK 0
# define O_NOCTTY 0

/* Builds on Windows MSYS2 environment did not recognize this macro: */
# ifndef TIOCM_ST
#  define TIOCM_ST	0x008
# endif
#endif	/* WIN32 */