syscalls/x86: Wire up COMPAT_SYSCALL_DEFINE0

syscalls/x86: Wire up COMPAT_SYSCALL_DEFINE0

BugLink: https://bugs.launchpad.net/bugs/1862227
commit cf3b83e19d7c928e05a5d193c375463182c6029a upstream.

x86 has special handling for COMPAT_SYSCALL_DEFINEx, but there was
no override for COMPAT_SYSCALL_DEFINE0.  Wire it up so that we can
use it for rt_sigreturn.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H . Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191008224049.115427-3-samitolvanen@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>