fix generic termios.h macro exposure/namespace issues

fix generic termios.h macro exposure/namespace issues

add EXTA, EXTB, CIBAUD, CMSPAR, XCASE macros and hide them as well as
CBAUD, ECHOCTL, ECHOPRT, ECHOKE, FLUSHO, PENDIN in standard mode.

the new macros are both in glibc termios.h and in linux asm/termbits.h,
the later also contains IBSHIFT and BOTHER, those were not added.

these are not standard macros, but some of them are in the reserved
namespace so could be exposed, the ones which are not reserved are
CIBAUD, CMSPAR and XCASE (which was removed in issue 6), the rest
got hidden to be consistent with glibc.