lttng: syscall instrumentation

x86-32 and x86-64 system call instrumentation, along with the
lttng-syscalls-generate-headers.sh script that generates the headers
from the system call list. See README for details.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>