decklink: add the SDK headers and build for Windows/Linux/macOS
Includes misc fixes for Windows compilation and many compilation warnings.
The SDK used has a Boost License which is MIT-like and GPL2v compatible. It's the September 2019 version.
The path of the SDK is kept as the original to keep compatibility with the official SDK. That means we have to enable it manually for each target. We could detect the right folder to use for each platform but we need to do it in configure.ac.
The DeckLink plugins are now built on Windows, Linux and macOS. The code has not been tested on a device.
Putting as draft for now as I'd like to check whether we really need $(LIBDL) -lpthread
on Linux/macOS.
Actually the .cpp helper code that needs to be loaded in Linux do use pthread_once()
and dlopen()
and macOS uses pthread_once()
. So they are needed for that glue code.