tracing: Fix syscall tracing on !HAVE_FTRACE_SYSCALLS architectures

The new syscall_regfunc()/unregfunc() functions rely on
the existence of TIF_SYSCALL_FTRACE - but that TIF flag
is only offered by HAVE_FTRACE_SYSCALLS.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/tracepoint.c

@@ -579,6 +579,8 @@ __initcall(init_tracepoints);
 
 #endif /* CONFIG_MODULES */
 
+#ifdef CONFIG_FTRACE_SYSCALLS
+
 static DEFINE_MUTEX(regfunc_mutex);
 static int sys_tracepoint_refcount;
 
@@ -615,3 +617,4 @@ void syscall_unregfunc(void)
 	}
 	mutex_unlock(&regfunc_mutex);
 }
+#endif