Flatten TIOCGWINSZ on OpenBSD.
Flatten TIOCGWINSZ on OpenBSD.

On this platform, the TIOCGWINSZ ioctl identifier is a complex macro.
Since we don't have a C bridging header obviously available to get the
flattened value, supply is the flattened value obtained elsewhere. This
is of course brittle but this is the simplest way around this for now.

Compare #291 in swift-argument-parser.

apple/swift-tools-support-core,apple/swift-tools-support-core,apple/swift-tools-support-core,apple/swift-tools-support-core