[aot] use g_error instead of fprintf + exit(1).

[aot] use g_error instead of fprintf + exit(1).

printfs don't always show up in the iOS device log, and exit(1) does
not create a crash report, making these conditions hard to debug
(all you get is "app X exited with code 1", and then you need to
attach a native debugger and break on 'exit' to figure out more).

g_error will end up producing output using NSLog (which always
shows up in the device log), and a crash report as well, making
debugging a lot easier.