<OS>_VERSION_MAX_ALLOWED indicates what version is available in
the SDK, while <OS>_VERSION_MIN_REQUIRED is the version we can
assume is available, i.e. similar to what is set with e.g.
-miphoneos-version-min on the command line.
This fixes build errors like these:
src/libavdevice/avfoundation.m:788:37: error: 'AVCaptureDeviceTypeContinuityCamera' is only available on macOS 14.0 or newer [-Werror,-Wunguarded-availability-new]
[deviceTypes addObject: AVCaptureDeviceTypeContinuityCamera];
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/AVFoundation.framework/Headers/AVCaptureDevice.h:551:38: note: 'AVCaptureDeviceTypeContinuityCamera' has been marked as being introduced in macOS 14.0 here, but the deployment target is macOS 13.0.0
AVF_EXPORT AVCaptureDeviceType const AVCaptureDeviceTypeContinuityCamera API_AVAILABLE(macos(14.0), ios(17.0), macCatalyst(17.0), tvos(17.0)) API_UNAVAILABLE(visionos) API_UNAVAILABLE(watchos);
^
Alternatively, we could use these more modern APIs, if enclosed
in suitable @available() checks.
081d69b78d