Searching CBAUD provided the answer. Rather interesting.

Seems CBAUD is but one of the many possibilities to use when setting the c_cflag member

Never initialize the c_cflag (or any other flag) member directly; you should always use the bitwise AND, OR, and NOT operators to set or clear bits in the members. Different operating system versions (and even patches) can and do use the bits differently...

The full text and table of constants for the c_cflag member is here https://wiki.control.fel.cvut.cz/pos/cv5/doc/serial.html