Ah, it appears to be -target: xcrun --sdk appletvsimulator clang -isysroot $(xcrun --sdk appletvsimulator --show-sdk-path) -target arm64-apple-tvos13.0-simulator test.c

6 years late, but I've just experienced this and it's the Info.plist settings: Supported interface orientations (iPad) which included all possible orientations despite setting just Landscape in the Build Settings. It's been this way for as long as I can remember, but I don't know why... Anyway delete the orientations you don't want and ensure the iOS Simulator has Device > Rotate Device Automatically turned on and you should be golden.