Split syscall tracepoint generation in their own files

Split syscall tracepoint generation in their own files

This commit tracepoint generation of the 4 different types of syscalls
(entry, exit, entry_compat, and exit_compat) each in their own .c file.

The compilation time of the lttng-modules projects is currently
dominated by the compilation of the src/lttng-syscalls.o object.
This is caused by the extensive use of macros to generate tracepoint for
all syscalls. This also uses a lot of memory making the compilation of
the project tedious on system with low memory.

This allows for parallelization of the compilation which offers 2
improvements: Reduction of compilation time and reduction of the memory
usage.

In term of compilation time, on my 4 cpus laptop, I measured a 15sec
(20%) speedup over 10 runs when using all 4 cpus (make -j4).

On a larger machine (16 cpus), I measured 30sec (60%) speedup when using
all 16 cpus.

In term of memory usage, I was able to compile the project on a virtual
machine with 500MB of memory without hitting memory exhaustion errors.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I025a4c36ef16b935be2a86f5b6649526752a7393