Also the iOS SDK isn’t freely available, so you’d have to copy that out of an Xcode installation… but given enough time and effort, you could almost certainly hack together a cross-compilation config for Clang that compiles an unsigned iOS app on Linux. Signing it might in fact be the bigger issue, since I’m not aware of any tools that sign Mach-O binaries on Linux.
Also the iOS SDK isn’t freely available, so you’d have to copy that out of an Xcode installation… but given enough time and effort, you could almost certainly hack together a cross-compilation config for Clang that compiles an unsigned iOS app on Linux. Signing it might in fact be the bigger issue, since I’m not aware of any tools that sign Mach-O binaries on Linux.