x86/signal: Cleanup get_nr_restart_syscall()

Check for TS_COMPAT instead of TIF_IA32 to distinguish ia32
tasks from 64-bit tasks.

Check for __X32_SYSCALL_BIT iff CONFIG_X86_X32_ABI is defined.

Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Elvira Khabirova <lineprinter0@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160111145515.GB29007@altlinux.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>