./configure script detects macos specific system headers
(IOKit/serial/ioss.h and sys/ttycom.h) that are not available
during compile time. There is no way to pass ac_cv_* vars to
./configure script due to perl wrappers

To fix this issue, fake(empty) headers provided during compile
time if build host is MacOS

Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>