A "compat" entry in the syscall tables means to use a different entry on
32-bit and 64-bit builds.

This only makes sense for syscalls that exist in the first place in 32-bit
builds, so disallow it for anything other than i386.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/4b7565954c5a06530ac01d98cb1592538fd8ae51.1562185330.git.luto@kernel.org