[TIMOB-28525] iOS: Cannot run apps with non-arm64 modules on Apple Silicon (even with Rosetta)

This will become a very common issue over the next few months as more Macs will run on the M1/MX chips: The build fails due to the arm64 architecture. In the native world, Apple resolves this by providing Rosetta, an architecture bridge that allows apps to be started in x86_64 (Intel) mode. So practically, users can just start their VSCode or Terminal with Rosetta (right click > Info > "Use Rosetta") and the app would compile with x86_64. But currently, the Titanium CLI uses process.arch to detect the architecture, which causes a problem, because it still detects arm64 and therefore fails early, although the build would run through. To fix this, the command uname -a can be used and returns the actual used process architecture. And since iOS apps don't run on Windows anyway, we don't have to fear Windows compatibility for the command.